HK1217053A1

HK1217053A1 - Authentication apparatus and method

Info

Publication number: HK1217053A1
Application number: HK16104958.4A
Authority: HK
Inventors: 羅伯特‧萊爾德‧斯圖爾特; 罗伯特‧莱尔德‧斯图尔特
Original assignee: 伊诺维亚薄膜有限公司
Priority date: 2013-05-10
Filing date: 2014-04-30
Publication date: 2016-12-16
Also published as: EP2994894A1; HK1217243A1; SG11201508539TA; US20160078707A1; MX346858B; AU2014264400B2; SG11201508540YA; US9721416B2; MX2015015193A; WO2014181086A1; WO2014181088A1; HK1214393A1; KR20160007613A; US20160086411A1; GB201308434D0; CN105264577A; EP2994892A1; MX2015015192A; CN105264579A; AU2014264403A1

Abstract

The present invention provides an authentication apparatus operative to determine the authenticity of a polymer film, comprising an optically-based birefringence measuring arrangement operative to measure a first effect influenced by a birefringence characteristic of said film from a first angle comprising a non-normal angle to a plane of said film, and at least one of: a second angle; and a third angle; and wherein said apparatus is operative to: compare a value, or range of values, representative of said first effect as measured from said first angle with a value, or range of values representative of a specified first effect corresponding to a predetermined birefringence characteristic of an authentic polymer film for said first angle; compare a value, or range of values, representative of said first effect as measured from said at least one of said second and third angles with a value, or range of values representative of a specified first effect corresponding to a predetermined birefringence characteristic of an authentic polymer film for respective second and/or third angles; and output an authenticity signal indicative of authenticity or otherwise of said film based upon said comparisons. There are also provided one or more methods of determining the authenticity of a polymer film.

Description

Authentication apparatus and method

The present invention relates to an authentication apparatus and method, and in particular, but not exclusively, to an authentication apparatus and method for authenticating a polymer film.

Polymer films are increasingly being used as substrates in areas where security, authentication, identification and anti-counterfeiting are of paramount importance. Polymer-based products in such fields include, for example, banknotes, important documents (e.g., ID materials such as, for example, passports and landfills, stock and academic certificates), films and security cards used for packaging high-value goods for anti-counterfeiting purposes.

Polymer-based security materials have advantages in terms of safety, functionality, durability, cost effectiveness, cleanliness, processability, and environmental factors. Perhaps the most notable among these factors is the security advantage. Paper banknotes, for example, can be relatively easy to replicate and the incidence of counterfeit notes in countries with polymer-based banknotes is lower than in countries with paper banknotes. Banknotes based on polymers are also more durable and less prone to tearing.

Polymeric film-based security materials help incorporate a variety of visible and hidden security features. As the introduction of the first generation of polymeric banknotes was approximately 30 years ago, security features have included optically variable images (OVDs), hazy features, printed security feature security threads, embossing, transparent windows and diffraction gratings. In addition to the complex security features, there are more immediate advantages: if counterfeit makers are merely attempting to reproduce security materials (e.g. banknotes) using copiers, the high temperatures used in such machines will often cause the polymer-based material to melt or deform.

A variety of polymers may be used as the security substrate. Including polypropylene films. The three main methods for producing polypropylene films are the tenter method, the casting method, and the bubble method.

In the casting and tentering processes, polymer chips are typically placed in an extruder and heated so that the extrudate is driven from a slot die onto a chill roll to form a film (in the case of the casting process) or a thick polymer strip (in the case of the tentering process). In a tenter frame process, the thick polymeric tapes are then reheated and then stretched in the lengthwise direction (referred to as the "machine direction") and the widthwise direction (referred to as the "transverse direction") to form a film.

In the bubble process, the polymer is extruded through an annular die rather than through a slot die to form a relatively thick extrudate in the shape of a hollow cylinder or "drainpipe" through which air is blown. The annular mould is located on top of an apparatus which typically corresponds to several stories (e.g. 40 to 50 metres) in height. The extrudate moves downward and is sequentially heated so that it expands to form bubbles. The bubble is then divided into two half-bubbles, each of which can be individually used as a "single web" die; or alternatively, the two halves may be kneaded and laminated together to form a double thickness film (or the bubbles may collapse to form a double thickness film). Typically, there are three concentric rings at the die, such that the hollow cylinder is a three layer extrudate. For example, there may be a core layer of polypropylene with a terpolymer skin layer on one side and another terpolymer skin layer on the other side. In this case, the single web would consist of three layers (with polypropylene in the middle) and the double web would consist of five layers, since the middle layer would be the same skin layer (terpolymer) of each half-bubble. Many other possible arrangements and components are possible (e.g., in terms of number of rings, type of skin pernicity, type of core layer, etc.).

Thus, the bubble method is to produce a film (e.g., 10 to 100 microns in thickness) by forming bubbles, while the tenter method is to produce a film by stretching the material on a flat frame. In the bubble method, stretching occurs simultaneously in both the machine direction and the transverse direction, and the degree of stretching in both directions is substantially the same. Thus, the bubble process produces a film that is uniformly stretched, unlike and for some purposes outperforms tentered films. Biaxially oriented polypropylene (BOPP) films were made by the bubble process from the intel films company (Wigton, UK). In addition to polypropylene, other polymers (e.g., LLDPE, polypropylene/butene copolymers) can be formed into films using the bubble process.

It is well known to incorporate features into films used as substrates for security documents, identification documents or valuable documents and articles, which features are not readily apparent to a potential unauthorized user or counterfeit money manufacturer and which cannot be readily reproduced even if identified. The introduction of such security features may also be applicable to other indicia or items (e.g., admission documents and tickets) that require validation of authentication.

Previous authentication devices and methods use known security document substrate sheets that allow electromagnetic radiation to pass through (e.g., transparent in the visible region of the electromagnetic spectrum). It is known to produce security documents by printing an opaque ink onto a sheet of transparent plastics substrate material leaving a transparent window. The resulting window provides the disclosed security features that are apparent to the human eye. It is well known to print, etch or embed additional optical security features (e.g. optically variable images formed by diffraction gratings) onto or into the resulting transparent window to provide additional disclosed security features. It is known to provide automatic verification devices that can determine authenticity from the presence or absence of these additional optical security features, but such devices are typically complex and expensive.

WO2009/133390 discloses a method of validating a polymer film, which comprises measuring the birefringence of a core layer therein. Fig. 1 to 3 show components of an apparatus for different methods of observing birefringence, as disclosed in WO 2009/133390.

Birefringence or birefringence is a material property caused by the difference in refractive index of a material for two different polarizations (s-polarization and p-polarization) and between two axes in its surface plane.

The birefringent material splits light into ordinary O rays and very E rays when faced with polarized light (e.g., formed by light passing through a first polarizer), which are retarded by transmission through the birefringent material, but to a different degree. After transmission through a second polarizer at 90 ° with respect to the polarized light (e.g., at 90 ° with respect to the polarization orientation of the first polarizer), the two rays (i.e., the ordinary ray and the extraordinary ray) recombine and destructively or constructively interfere with each other. The effect produced is a variable transmission in the form of a sine wave, as the birefringent material rotates from a minimum (at 0 ° relative to the polarizer) to a maximum (at 45 ° relative to the polarizer). This occurs because at 0 and 90 the birefringent material is indeed the same as those polarizers in line with it, while at 45 the second polarization event occurs. The light passing through the first polarizer is rotated exactly 45 ° from the E-plane and O-plane of the birefringent material; thus, the birefringent material splits this light into O-rays and E-rays that are rotated 45 ° from the incident polarized light. Upon reaching the second polarizer (which itself is now rotated 45 ° from the new O-ray and E-ray), the two rays combine to pass through the second polarizer.

If supplemented by an initial forced partial rotation step, the polarized light can be effectively rotated by 90. If the birefringent material is rotated at other angles this will affect the portion of the polarized light in the birefringent material that can become O-rays or E-rays and will therefore also affect the portion of the light that is eventually transmitted by the second polarizer. As mentioned above, rotation of the central polarizer in practice allows light to have a sinusoidal intensity versus rotation angle of more than 90 °.

The O-rays and E-rays propagate in the birefringent material at different velocities (due to the different refractive indices in the birefringent material). If this difference is large enough and the path length through the birefringent material is long enough, the light will become completely out of phase at the different wavelengths. Upon recombination at the second polarizer, some colors will destructively interfere resulting in transmitted light having a color.

The birefringence is described by equation (1):

Δn＝n_x–n_y(1)

where Δ n is the birefringence, n_xIs a refractive index in the extraordinary plane, and n_yThe refractive index in the ordinary plane.

The effect of birefringence is the "rotation" and interference of polarized light, which is a product of birefringence and path length through the material.

The AMichel-levy interference color map defines interference colors from different orders of birefringence. An experimenter may use this map to estimate the birefringence of a material, and may estimate the retardation of a material from a comparison of the transmitted light color with the color on the map. Such a diagram is illustrated in fig. 12 for reference only. The figure is black and white and the full color version of the figure should be viewed for transmitted color.

The degree of delay can be described by equation (2):

r＝dΔn(2)

wherein: r is retardation (m), Δ n is birefringence, and d is path length (m).

The path length d remains the same for materials of substantially uniform thickness. Thus, a measurement of light passing through a material will indicate how much the birefringence of the material, and therefore how much more the material is oriented in one direction compared to the other.

Birefringence is induced in polymer films in three ways: crystal orientation, polymer chain orientation, and lattice distortion.

The refractive index is proportional to the material density; the polymeric material exists in both crystalline and amorphous forms, which are present in known proportions within a particular polymer type-polypropylene can be between 35% and 50% crystalline depending on its molecular weight range and its stereochemistry. During the bubble process, when the molten cast tube (thickness of 1mm) was quenched with chilled water, crystallization occurred; cooling is rapid and a temperature gradient occurs across the thickness of the film, giving the crystallization some directionality. Crystalline regions are formed throughout the cast tube, which are subsequently drawn into their final shape within the finished polymer during the drawing process. Birefringence is caused by the difference in length of the various dimensions of the crystalline regions and their orientation within the polymer; when the bubble polymer is stretched equally in both the machine and transverse directions, it is expected that this will eventually be balanced to produce low birefringence; however, the distribution of the crystalline regions is not uniform, resulting in a difference in birefringence over a distance of 1 to 3 mm.

The refractive index is also affected by the orientation of the polymer chains within the material; this has the greatest effect on the overall birefringence, which is proportional to the ratio between the machine direction stress and the transverse direction stress during stretching.

Finally, lattice distortion is theoretically the cause of birefringence, but is not necessarily important in soft, low-melting materials (e.g., polypropylene).

The resulting effect of the birefringence of the material manifests itself as a rotation of the polarization angle of light transmitted through the material; the effect is initiated via interfacial interactions and propagates via the birefringent material; the observed birefringence is the product of the initial interfacial interaction (i.e., angle of incidence) and the subsequent path length through the material.

As mentioned above, the birefringence effect is a product of the degree to which the film thickness and refractive index differ between the axes. The effect is visible if the film is placed between crossed polarizers and rotated 90 ° between a minimum (equivalent to no change in transmission from the crossed polarizers) to a maximum at 45 ° (where potentially light passing through a single polarizer would be literally transmitted).

Birefringence in the film is induced by the difference in orientation created between the machine and transverse directions; the resulting film has the two axes at 90 ° to each other, at which point the birefringence is at its minimum and 45 ° from either axis is at its maximum. Each material made by each known process will have the same properties (including polarizers) due to the nature of the film processing in the web and sheet.

Due to the prevalence of polymer orientation, a single measurement of birefringence at 45 ° is sufficient to determine the maximum of any film and any print from that film. The polarizer itself will also conform to this; thus, in the manufacture of a device (e.g., such a device), the polarizer should be sized such that it should be cut at 45 ° from the sheet of primary polarizer.

The method and apparatus disclosed in WO2009/133390 involves the use of a pair of spin polarisers oriented at 90 ° to each other. The polarizers are operable to rotate at the same rate, and the apparatus is operable to measure the intensity of light passing through a sample placed between the polarizers.

To distinguish designated authentic films from other films, the birefringence measurement method disclosed in WO2009/1333390 may be employed to allow a user to exclude other types of films (i.e., designated counterfeit films): BOPP films made by the tentering process are more oriented in the transverse direction than in the machine direction and therefore have significantly greater birefringence than BOPP films made by the double bubble process. The birefringence can be precisely controlled using a double bubble process and thus can provide a unique signature (signature) that can reject the film.

The method of WO2009/133390 allows the film to be secured as such. The disclosed method is used to observe certain inherent properties of the film without the addition of any additional security or identification features. This identification allows verification for safety purposes and also allows determination of the origin of the film.

The films referenced herein are generally sheet-like materials, and may be provided as individual sheets or web materials, which may then be processed (e.g., through a mold) to provide a sheet or article-like material. When reference is made to "film" in this specification, it is intended to include a sheet, article, or web of film unless explicitly stated otherwise.

As mentioned above, the method of WO2009/133390 is suitable for authenticating articles containing films made by the bubble process. The bubble process produces a film with balanced orientation, well-defined and uniform thickness, and other properties (high tensile strength, low elongation, high gloss and clarity, good puncture and flex crack resistance, oil and grease resistance, good water impermeability) that define the "signature" of the film indicating that it has been made by the bubble process.

To distinguish between films (e.g., BOPP films and other films), the overall thickness of the film can be measured as well as the thickness of individual layers (e.g., laminate layers). This allows the determination of specific characteristics that depend on a specific process (e.g., a bubble process). Additionally or alternatively, the film's unique birefringence signature can be evaluated and used to determine whether the film was made by a particular process and thus whether it is, for example, a genuine or counterfeit note. The birefringence depends on the anisotropy of the material, and films made by the bubble process have different anisotropy and hence different birefringence properties than films made by other processes. Furthermore, the precise conditions used in the bubble process will affect the birefringence signature.

WO2009/133390 recognizes that the inherent properties of films made by a particular process (e.g. the bubble process) are unique and act as a signature, rather than requiring the addition of security or identification features.

The actual counterfeit film is more likely to be purchased than the counterfeit manufacturer. There are several sources, which can be divided into three main groups:

1. cast or blown-cast films are made by extruding a polymer through a die onto chilled rolls. Blown films are made by extruding a polymer through a circular die and expanding gas bubbles in a semi-molten state. Cast & blown films are typically unoriented or slightly oriented and therefore have internal dimensional stability (i.e., they can be easily stretched), poor optics, and thickness control.

2. Mono-oriented film-a mono-oriented film is made by extrusion through a die and stretching in the machine direction. The mono-oriented film is highly oriented; which has poor optics and poor dimensional stability in the transverse direction.

3. Biaxially oriented film-biaxially oriented films are available from innovia films limited and many other suppliers. Commercial grade BOPP from many suppliers is generally made by a tentering process in which PP is extruded through a slot die onto chilled rolls, stretched in the machine direction over heated rolls, and stretched in the transverse direction in a tenter frame. Unlike BOPP made by the double bubble process, which is uniformly oriented in all directions, these films are anisotropic in nature.

While the method and apparatus of WO2009/133390 has been satisfactory and is believed to continue to be satisfactory for certain operating conditions, applicants have recognized that it would be desirable to increase the range of operating conditions to allow for use of the method and apparatus in particular applications and/or environments, and potentially for indicating the authenticity of film types made by other processes (e.g., real films formed by tentering processes). Applicants have also recognized that there would be a need to increase the ability to discriminate between different membrane types having similar measurable properties and to account for misaligned membranes in the apparatus. The applicant has also realised that it would be desirable to take into account variations in the quality of real films to inhibit BOPP bubble process films from having the opportunity to develop false negatives in which the manufacturing process for those films is poorly controlled (or indeed for any other type of specified real film, regardless of the process by which it is manufactured).

The present invention has been devised in view of the above considerations.

According to an aspect of the present invention there is provided an authentication apparatus operable to determine the authenticity of a polymer film, comprising an optically based optical refractive index measurement arrangement operable to measure a first effect influenced by a birefringence characteristic of the film from a first angle comprising a non-perpendicular angle to the plane of the film and at least one of a second angle and a third angle; and wherein the apparatus is operable to: comparing a value or range of values representing a first effect as measured from a first angle to a value or range of values representing a specified first effect corresponding to a predetermined birefringence characteristic of an authentic polymer film for the first angle; comparing a value or range of values representative of the first effect as measured from the at least one of the second and third angles to a value or range of values representative of a specified first effect corresponding to a predetermined birefringence characteristic of an authentic polymer film for the respective second and/or third angles; and outputting an authenticity signal indicative of the authenticity or otherwise of the film based on the comparison.

The present invention allows the film to be secured as is. The specific inherent properties of the film are observed in the present invention without the addition of any additional security or identification features. This identification allows verification for safety purposes and also allows determination of the origin of the film. In addition, the apparatus may be adapted to distinguish between films formed by the first process and films formed by other processes. For example, in the case where the genuine article comprises a substrate formed by a bubble process and the counterfeit article in general comprises a substrate formed by a tenter frame or casting process.

Optionally, the second angle may comprise a non-perpendicular angle to the plane of the film, and the third angle may comprise a perpendicular angle to the plane of the film.

Optionally, the apparatus is operable to distinguish between membranes made by a bubble process and membranes made by a different process.

Optionally, the optical-based birefringence measurement arrangement may include: an emitter positioned and operable to illuminate a first side of the film positioned in a measurement region of the apparatus with electromagnetic radiation; a first polarizer positioned between the first emitter and the film first side such that at least a portion of the electromagnetic radiation emitted by the first emitter passes therethrough; a first detector positioned on the film second side and operable to receive electromagnetic radiation from the emitter transmitted through the film and transmitted from the film second side at a first angle and at least one of a second angle and a third angle; a second polarizer positioned between the second side of the film and the first detector such that at least a portion of the electromagnetic radiation transmitted through the film passes therethrough, wherein the first detector is operable to output a signal indicative of a first effect as measured based on the electromagnetic radiation transmitted from the second side of the film at the first angle and at least one of the second angle and the third angle.

Optionally, the first detector may be movable relative to the second side of the film to be positioned at a first position to receive electromagnetic radiation from the emitter that is transmitted through the film and transmitted from the second side of the film at a first angle, and may be further movable to a second position and/or a third position to receive electromagnetic radiation from the emitter that is transmitted through the film and transmitted from the second side of the film at a corresponding second angle and/or a third angle.

Optionally, the apparatus may further comprise: a second detector positioned on the second side of the film and operable to receive electromagnetic radiation from the emitter that is transmitted through the film and transmitted from the second side of the film at a second angle; and/or a third detector positioned on the second side of the film and operable to receive electromagnetic radiation from the emitter that is transmitted through the film and transmitted from the second side of the film at a third angle; wherein:

the second detector is operable to output a signal indicative of a first effect as measured based on electromagnetic radiation transmitted from the second side of the film at a second angle; and/or the third detector is operable to output a signal indicative of the first effect as measured based on electromagnetic radiation transmitted from the second side of the film at a third angle.

Optionally, the first angle may comprise one of: (i) an angle described by vector [101] with respect to the film; and (ii) an angle described by the vector [111] with respect to the film. Further optionally, the second angle may comprise another one of: (i) an angle described by vector [101] with respect to the film; and (ii) an angle described by the vector [111] with respect to the film.

Optionally, the output signal output by the first detector may be proportional to the intensity of the received transmitted electromagnetic radiation. Further optionally, the output signal output by the second detector and/or the third detector (where present) may be proportional to the intensity of the received transmitted electromagnetic radiation.

Optionally, the first detector may be operable to communicate the output signal to a processor operable to compare output signal values representing a first effect as measured from a first angle to a value or range of values representing a specified first effect corresponding to a predetermined birefringence characteristic of an authentic polymer film for the first angle. Further optionally, the second detector may be operable to communicate the output signal to a processor operable to compare output signal values representative of the first effect as measured from the second angle with a value or range of values representative of a specified first effect corresponding to a respective predetermined birefringence characteristic of the authentic polymer film for the second angle; and/or the third detector may be operable to communicate the output signal to a processor operable to compare output signal values representative of the first effect as measured from the third angle with a value or range of values representative of a specified first effect corresponding to a respective predetermined birefringence characteristic of the authentic polymer film for the third angle. Still further optionally, the value or range of values may include at least one expected first detector output signal value representative of electromagnetic radiation transmitted from the second side of the film at a first angle and received by the first detector with an actual film positioned in the measurement region. Still further optionally, the method further comprises,

the value or range of values may include at least one expected second detector output signal value representative of electromagnetic radiation transmitted from the second side of the film and received by the second detector with an actual film positioned in the measurement region; and/or the value or range of values may comprise at least one expected third detector output signal value representative of electromagnetic radiation transmitted from the second side of the film and received by the third detector in the event that an actual film is positioned in the measurement region.

Optionally, the apparatus may further comprise an optical-based measurement arrangement operable to measure a second effect affected by at least one other optical property of the film (e.g. transmittance) at a first angle comprising a non-perpendicular angle to the plane of the film and at least one of a second angle and a third angle, and wherein the apparatus is operable to: comparing a value or range of values representing a second effect as measured at a first angle comprising a non-perpendicular angle to the film surface and at least one of a second angle and a third angle with a value or range of values representing a specified second effect corresponding to a predetermined other optical characteristic of the authentic polymer film for the respective first angle and the respective second and/or third angle, and outputting an authenticity signal indicating authenticity or other aspect of the film based on: comparison of birefringence measurements as described above and below; and/or a comparison of a value or range of values of a second effect as measured at a first angle comprising a non-perpendicular angle to the film plane and at least one of a second angle and a third angle with a corresponding value or range of values representing a specified second effect corresponding to a predetermined other optical characteristic of the real polymer film for the corresponding first angle and the corresponding second angle and/or third angle.

Optionally, the second polarizer may be controllably oriented to achieve polarization in one of the following directions: a first direction transverse to the direction of the first polarizer; and a second direction identical to the direction of the first polarizer; wherein the first detector and/or optionally the second detector and/or the third detector is operable to: measuring a first effect affected by the birefringence characteristics of the film when the second polarizer is oriented so as to achieve polarization in a first direction transverse to the direction of the first polarizer; and measuring a second effect affected by other optical properties of the film when the second polarizer is oriented so as to achieve polarization in a second direction that is the same as the direction of the first polarizer.

Optionally, the first detector and/or optionally the second detector and/or the third detector may be operable to: outputting a first signal representative of the first effect as measured; and outputting a second signal representative of the second effect as measured. Further optionally, the first and second output signals output by the first and/or optionally second and/or third detectors may be proportional to the intensity of the received transmitted electromagnetic radiation. Still further optionally, the first detector and/or optionally the second detector and/or the third detector may be operable to communicate the first output signal and the second output signal to a processor, the processor operable to: comparing the value of the first output signal with a value or range of values representing a specified first effect; and comparing the value of the second output signal to a value or range of values representing a specified second effect, the specified second effect corresponding to the predetermined film transmittance.

Optionally, if the first output signal value or range of values has a level distinguishable from the first output signal value or range of values representing an effect affected by the background condition, the processor may be operable to output the authenticity signal based on a comparison of the value or range of values of the second output signal with the value or range of values representing the specified second effect.

That is, if a comparison of the value of the first output signal by the processor with a value or range of values representative of a specified first effect (corresponding to a predetermined birefringence characteristic of an authentic polymer film) results in an inconclusive authenticity determination by the processor (because the first output signal value is, for example, very low or distinguishable from background noise), the processor may be operable to provide an indication of authenticity determination based on a comparison of the value of the second output signal with a value or range of values representative of a specified second effect (for example, a predetermined film transmittance).

Optionally, the value or range of values may comprise at least one expected first detector and/or optionally second detector and/or third detector output signal value representing electromagnetic radiation transmitted from the film second side and received by the first detector and/or optionally second detector and/or third detector when the second polarizer is oriented so as to achieve polarization in the first direction and in the second direction, respectively, with an actual film positioned in the measurement region.

Optionally, the processor may be further operable to: calculating a difference between a value of the first output signal and a value of the second output signal; calculating a modified difference value by halving the difference value; calculating a birefringence representative value by subtracting the modified difference value from the second output signal value; comparing the birefringence representation value with a value or range of values representing the specified first effect; and outputting an authenticity signal indicative of the authenticity or otherwise of the film based on the comparison.

Optionally, the optical-based birefringence measurement arrangement may be further operable to measure a third effect within at least a portion of the electromagnetic spectrum and at least one of the first angle and the second and third angles, as influenced by the birefringence characteristics of the film, and wherein the apparatus is operable to: comparing a value or range of values representing a third effect as measured at the first angle and at least one of the second angle and the third angle to a corresponding value or range of values representing a specified third effect corresponding to a predetermined birefringence characteristic of an authentic polymer film at the corresponding first angle and the corresponding second angle and/or third angle for the same at least a portion of the electromagnetic spectrum; and outputting an authenticity signal indicative of the authenticity or otherwise of the film based on the comparison.

Optionally, the measurement of the third effect may comprise a monochromatic measurement (e.g., a color measurement in which a specific color of illumination lamp is used).

Optionally, the first detector and/or optionally the second detector and/or the third detector may be configured to selectively respond to the at least a portion of the electromagnetic spectrum.

Optionally, the first detector and/or optionally the second detector and/or the third detector may be of a controllable type to alter its detection range to correspond to said at least part of the electromagnetic spectrum.

Optionally, the first detector and/or optionally the second detector and/or the third detector may be preselected to detect electromagnetic radiation from the at least a portion of the electromagnetic spectrum.

Optionally, each of the first detector and/or optionally the second detector and/or the third detector may comprise an array of at least two sub-detectors, a first of the at least two sub-detectors being operable to detect electromagnetic radiation from a first portion of the electromagnetic spectrum and a second of the at least two sub-detectors being operable to detect electromagnetic radiation from a second portion of the electromagnetic spectrum.

Optionally, the first sub-detector may be controllable to alter its detection range to correspond to a first portion of the electromagnetic spectrum, and the second sub-detector may be controllable to alter its detection range to correspond to a second portion of the electromagnetic spectrum.

Optionally, a first sub-detector may be preselected to detect electromagnetic radiation from a first portion of the electromagnetic spectrum, and a second sub-detector may be preselected to detect electromagnetic radiation from a second portion of the electromagnetic spectrum.

Optionally, the apparatus may further comprise at least one filter arranged to mask at least another portion of the electromagnetic spectrum and transmit the at least a portion of the electromagnetic spectrum for reception by the first detector and/or optionally the second detector and/or the third detector.

Optionally, the emitter or optionally several emitters may be controllable to emit electromagnetic radiation in the at least a portion of the electromagnetic spectrum.

Optionally, the emitter or optionally several emitters may be preselected to emit electromagnetic radiation in the at least a portion of the electromagnetic spectrum.

Optionally, the emitter or optionally emitters may be operable in a first mode to emit white light and in a second mode to emit colored light.

Optionally, the apparatus may be operable in a first mode to control the first emitter to emit white light and in a second mode to control the second emitter to emit colored light.

Optionally, in the first mode, the apparatus may be operable to indicate whether the polymer film under test comprises a first true type or at least a second true type of polymer film based on the output signal of the first detector, and further wherein, in response to the output signal indicating that the polymer under test is a type different from the first true type, the apparatus is operable to implement the second mode and to indicate whether the polymer film under test comprises the at least second true type or other type of polymer film based on the output signal of the first detector in both the first and second modes.

Optionally, in the first mode, the apparatus is operable to: comparing a value or range of values representing a third effect as measured at the first angle and at least one of the second angle and the third angle to a value or range of values representing a specified third effect corresponding to a predetermined birefringence characteristic of the first genuine type of polymer film at the respective first angle and the respective second angle and/or third angle; and outputting a classification signal indicating that the membrane includes the first true type or the other type based on the comparison.

Optionally, the apparatus is operable to: in case the value representing the third effect as measured at the first, second or third angle is below a corresponding first mode first threshold value for the first, second or third angle, the output indicates that the film comprises the first true type, the corresponding first mode first threshold value representing an upper limit of the specified first effect for the first true type of film.

Optionally, the apparatus is operable to: in case the value representing the third effect as measured at the first, second or third angle is both above the corresponding first mode first threshold value for the first, second or third angle and not within a value range between the corresponding first mode second threshold value for the first, second or third angle and the corresponding first mode third threshold value for the first, second or third angle, the output indicates that the film comprises the non-true type.

Optionally, the apparatus is operable to: the second mode is implemented in case the value representing the third effect as measured in the first mode at the first, second or third angle is between the corresponding first mode second threshold for the first, second or third angle and the corresponding first mode third threshold for the first, second or third angle.

Optionally, the apparatus is operable to: in case the value representing the third effect as measured at the first, second or third angle is within a range of values between a corresponding second mode first threshold for the first, second or third angle and a corresponding second mode second threshold for the first, second or third angle, the range of values representing a specified third effect for the second true type of film, the output indicates that the film comprises the second true type.

Optionally, the apparatus may further comprise an optically-based birefringence imaging arrangement for imaging the birefringence pattern of the film at a first angle and at least one of a second angle and a third angle, and wherein the apparatus is operable to: comparing an image of the birefringence pattern with a corresponding image representing a predetermined birefringence pattern of the authentic polymer film at a corresponding first angle and corresponding second and third angles; and outputting an authenticity signal indicative of the authenticity or otherwise of the film based on the comparison.

Optionally, the optically-based birefringence imaging arrangement may include: an emitter positioned and operable to illuminate a first side of the film positioned in a measurement region of the apparatus with electromagnetic radiation; a first polarizer positioned between the first emitter and the film first side such that at least a portion of the electromagnetic radiation emitted by the first emitter passes therethrough; an imaging device positioned on the film second side and operable to receive electromagnetic radiation from the emitter transmitted through the film and transmitted from the film second side; a second polarizer positioned between the second side of the film and the imaging device such that at least a portion of the electromagnetic radiation transmitted through the film passes therethrough, wherein the imaging device is operable to: outputting data representing the imaged birefringence pattern based on electromagnetic radiation transmitted from the second side of the film and received at the imaging device.

Optionally, the imaging device may be operable to output data representative of the imaged birefringence pattern to a processor operable to compare the output data with a data set representative of a predetermined birefringence pattern.

Optionally, at least one of the emitter, the first polarizer and the second polarizer may have in common with the optical based birefringence measurement arrangement and/or the/those of the optical based measurement arrangement.

Optionally, the emitter may comprise a white light source.

Optionally, the imaging device may include a photosensitive array.

Optionally, the apparatus may further comprise an optical response modifier arranged to modify the first effect to introduce a predetermined amount of offset to a value or range of values representative of the effect as measured, wherein the optical-based birefringence measurement arrangement is operable to measure the first effect as modified.

Optionally, the optical response modifier may be positioned in a beam path of the electromagnetic radiation between the emitter and the first detector and/or optionally the second detector and/or the third detector, and further wherein the first detector and/or optionally the second detector and/or the third detector may be operable to measure the first effect.

Optionally, the first detector and/or optionally the second detector and/or the third detector may be operable to output a signal representative of the first effect as modified.

Optionally, the first detector and/or optionally the second detector and/or the third detector may be operable to communicate the output signal to a processor, which may be operable to compare a value of the output signal representing the first effect as modified to a value or range of values representing a specified first effect corresponding to a predetermined birefringence characteristic of an authentic polymer film and as modified by the same optical response modifier.

Optionally, the apparatus may be operable to receive an article comprising a polymeric film forming at least a portion of a substrate of the article.

According to another aspect of the present invention there is provided banknote validating apparatus comprising apparatus including any one or more of the above features, wherein the apparatus is operable to determine the authenticity of a banknote comprising a polymeric film which forms at least part of a substrate of the banknote.

An apparatus comprising any one or more of the features described above may be used to determine the authenticity of a polymer film.

According to another aspect of the present invention, there is provided a method of determining the authenticity of a polymer film, comprising: measuring a first effect affected by a birefringence characteristic of the film from a first angle comprising a non-perpendicular angle to a plane of the film and at least one of a second angle and a third angle; comparing a value or range of values representing a first effect as measured from a first angle to a value or range of values representing a specified first effect corresponding to a predetermined birefringence characteristic of an authentic polymer film for the first angle; comparing a value or range of values representative of the first effect as measured from the at least one of the second and third angles to a value or range of values representative of a specified first effect corresponding to a predetermined birefringence characteristic of an authentic polymer film for the respective second and/or third angles; and outputting an authenticity signal indicative of the authenticity or otherwise of the film based on the comparison.

Optionally, the second angle may be a non-perpendicular angle to the plane of the film, and the third angle may be a perpendicular angle to the plane of the film.

Optionally, the method may further comprise indicating whether the polymer film is made by a bubble process or a different process.

Optionally, the method may further comprise: illuminating a first side of the film positioned in a measurement region of the apparatus with electromagnetic radiation polarized by a first polarizer positioned between a first emitter and the first side of the film such that at least a portion of the electromagnetic radiation emitted by the first emitter passes therethrough; receiving, at a first detector positioned on a second side of the film, electromagnetic radiation from the emitter that is transmitted through the film at a first angle and at least one of a second angle and a third angle and polarized by a second polarizer positioned between the second side of the film and the first detector; and outputting a signal representing a first effect as measured based on electromagnetic radiation transmitted from the second side of the film at the first angle and at least one of the second angle and the third angle.

Optionally, the method may further comprise: positioning a first detector at a first position to receive electromagnetic radiation from the emitter that is transmitted through the film and transmitted at a first angle from a second side of the film; and moving the first detector to the second position and/or the third position to receive electromagnetic radiation from the emitter that is transmitted through the film and transmitted from the second side of the film at the respective second angle and/or third angle.

Optionally, the method may further comprise: providing a second detector on the second side of the film for receiving electromagnetic radiation from the emitter that is transmitted through the film and transmitted from the second side of the film at a second angle; and/or providing a third detector positioned on the second side of the film for receiving electromagnetic radiation from the emitter that is transmitted through the film and transmitted at a third angle from the second side of the film; and outputting a signal from the second detector, the signal being representative of the first effect as measured based on electromagnetic radiation transmitted at a second angle from the second side of the film; and/or output a signal from the third detector, the signal being indicative of the first effect as measured based on electromagnetic radiation transmitted from the second side of the film at a third angle.

Optionally, the method may further comprise: communicating the output signal to a processor; the output signal values representing the first effect as measured from the first angle are compared to a value or range of values representing a specified first effect corresponding to a predetermined birefringence characteristic of an authentic polymer film for the first angle.

Optionally, the value or range of values may include at least one expected first detector output signal value representative of electromagnetic radiation transmitted from the second side of the film at a first angle and received by the first detector with an actual film positioned in the measurement region.

Optionally, the output signal output by the second detector and/or the third detector may be proportional to the intensity of the received transmitted electromagnetic radiation.

Optionally, the method may further comprise: communicating the output signal from the second detector to the processor; comparing output signal values representing the first effect as measured from the second angle with values or ranges of values representing specified first effects corresponding to respective predetermined birefringence characteristics of the authentic polymer film for the second angle; and/or communicating an output signal from the third detector to the processor; the output signal values representing the first effect as measured from the third angle are compared to a value or range of values representing a specified first effect corresponding to a respective predetermined birefringence characteristic of the authentic polymer film for the third angle.

Optionally: the value or range of values may include at least one expected second detector output signal value representative of electromagnetic radiation transmitted from the second side of the film and received by the second detector with an actual film positioned in the measurement region; and/or the value or range of values may comprise at least one expected third detector output signal value representative of electromagnetic radiation transmitted from the second side of the film and received by the third detector in the event that an actual film is positioned in the measurement region.

Optionally, the method may further comprise: measuring a second effect affected by at least one other optical characteristic of the film at a first angle comprising a non-perpendicular angle to the plane of the film and at least one of a second angle and a third angle; comparing a value or range of values representing a second effect as measured at the first angle and at least one of the second angle and the third angle with a value or range of values representing a specified second effect corresponding to a predetermined other optical characteristic of the real polymer film at the respective first angle and the respective second angle and/or third angle; and outputting an authenticity signal indicative of authenticity or otherwise of the film based on: comparison of birefringence measurements as described above and below; and/or a comparison of a value or range of values of the second effect as measured at the first angle and at least one of the second angle and the third angle with a corresponding value or range of values representing a specified second effect corresponding to a predetermined other optical characteristic at the corresponding first angle and the corresponding second angle and/or third angle.

Optionally, the method may further comprise: the second polarizer is oriented so as to achieve polarization in one of the following directions: a first direction transverse to the direction of the first polarizer; and a second direction identical to the direction of the first polarizer; a first effect influenced by the birefringence properties of the film is measured when the second polarizer is oriented so as to achieve polarization in a first direction transverse to the direction of the first polarizer, and a second effect influenced by other optical properties of the film is measured when the second polarizer is oriented so as to achieve polarization in a second direction that is the same direction as the direction of the first polarizer.

Optionally, the method may further comprise: outputting a first signal representative of the first effect as measured; and outputting a second signal representative of the second effect as measured.

Optionally, the first and second output signals output by the first and/or optionally second and/or third detectors may be proportional to the intensity of the received transmitted electromagnetic radiation.

Optionally, the method may further comprise: communicating the first output signal and the second output signal to a processor; comparing the value of the first output signal with a value or range of values representing a specified first effect; and comparing the value of the second output signal to a value or range of values representing a specified second effect, the specified second effect corresponding to the predetermined film transmittance.

Optionally, if the first output signal value or range of values has a level distinguishable from the first output signal value or range of values representing an effect affected by the background condition, the processor is operable to output the authenticity signal based on a comparison of the value or range of values of the second output signal with the value or range of values representing the specified second effect.

Optionally, the method may further comprise: calculating a difference between a value of the first output signal and a value of the second output signal; calculating a modified difference value by halving the difference value; calculating a birefringence representative value by subtracting the modified difference value from the second output signal value; comparing the birefringence representation value with a value or range of values representing the specified first effect; and outputting an authenticity signal indicative of the authenticity or otherwise of the film based on the comparison.

Optionally, the method may further comprise: measuring a third effect influenced by a birefringence characteristic of the film within at least a portion of the electromagnetic spectrum and at the first angle and at least one of the second angle and the third angle; comparing a value or range of values representing a third effect as measured at the first angle and the second angle and/or the third angle with a corresponding value or range of values representing a specified third effect corresponding to a predetermined birefringence characteristic of an authentic polymer film at the corresponding first angle and the corresponding second angle and/or third angle for the same at least a portion of the electromagnetic spectrum; and outputting an authenticity signal indicative of the authenticity or otherwise of the film based on the comparison.

Optionally, the measuring of the third effect may comprise a monochromatic measurement.

Optionally, the method may further comprise: the first detector and/or optionally the second detector and/or the third detector are configured to selectively respond to the at least a portion of the electromagnetic spectrum.

Optionally, the method may further comprise: the first detector and/or optionally the second detector and/or the third detector are controlled to alter their detection range to correspond to the at least a portion of the electromagnetic spectrum.

Optionally, the method may further comprise: the first detector and/or optionally the second detector and/or the third detector are preselected to detect electromagnetic radiation from the at least a portion of the electromagnetic spectrum.

Optionally, the method may further comprise: providing an array of at least two sub-detectors as each of the first and/or optionally the second and/or third detectors; and detecting electromagnetic radiation from a first portion of the electromagnetic spectrum at a first one of the at least two sub-detectors; detecting electromagnetic radiation from a second portion of the electromagnetic spectrum at a second of the at least two sub-detectors.

Optionally, the method may further comprise: controlling the first sub-detector to alter its detection range to correspond to a first portion of the electromagnetic spectrum; and controlling the second sub-detector to alter its detection range to correspond to the second portion of the electromagnetic spectrum.

Optionally, the method may further comprise: preselecting a first sub-detector to detect electromagnetic radiation from a first portion of the electromagnetic spectrum; and pre-selecting a second sub-detector to detect electromagnetic radiation from a second portion of the electromagnetic spectrum.

Optionally, the method may further comprise: masking at least another portion of the electromagnetic spectrum to transmit the at least one portion of the electromagnetic spectrum for reception by the first detector and/or optionally the second detector and/or the third detector.

Optionally, the method may further comprise: controlling the emitter or optionally emitters to emit electromagnetic radiation in the at least a portion of the electromagnetic spectrum.

Optionally, the method may further comprise: the emitter or optionally emitters are preselected to emit electromagnetic radiation in the at least a portion of the electromagnetic spectrum.

Optionally, the method may further comprise: operating the emitter or optionally emitters in a first mode to emit white light; and operating the emitter or optionally emitters in a second mode to emit colored light.

Optionally, the method may further comprise: controlling the first emitter to emit white light in a first mode; and controlling the second emitter to emit colored light in the second mode.

Optionally, the method may comprise: in the first mode, whether the polymer film under test comprises a first true type or at least a second true type is indicated based on the output signal of the first detector and/or optionally the second detector and/or the third detector, and further wherein, in response to the output signal indicating that the polymer under test is a type different from the first true type, implementing the second mode and indicating whether the polymer film under test comprises the at least second true type or other type based on the output signal of the first detector in both the first and second modes and/or optionally the output signal of the second detector and/or the third detector in both the first and second modes.

Optionally, in the first mode, the method may further comprise the steps of: comparing a value or range of values representing a third effect as measured at the first angle and the second angle and/or the third angle to a value or range of values representing a specified third effect corresponding to a predetermined birefringence characteristic of the first genuine type of polymer film at the respective first angle and the respective second angle and/or the third angle; and outputting a classification signal indicating that the membrane includes the first true type or the other type based on the comparison.

Optionally, the method may further comprise: in case the value representing the third effect as measured at the first angle and the second and/or third angle is below a corresponding first mode first threshold value for the first, second or third angle, the classification signal indicating that the film comprises the first true type is output, the corresponding first mode first threshold value representing an upper limit of the specified first effect for films of the first true type.

Optionally, the method may further comprise: in case the value representing the third effect as measured at the first angle and the second and/or third angle is both above the corresponding first mode first threshold value for the first, second or third angle and not within a value range between the corresponding first mode second threshold value for the first, second or third angle and the corresponding first mode third threshold value for the first, second or third angle, the output indicates that the film comprises the non-true type.

Optionally, the method may further comprise: the second mode is implemented in case the value representing the third effect as measured in the first mode at the first angle and the second angle and/or the third angle is between a corresponding first mode second threshold for the first, second or third angle and a corresponding first mode third threshold for the first, second or third angle.

Optionally, the method may further comprise: in case the value representing the third effect as measured at the first, second or third angle is within a range of values between a corresponding second mode first threshold for the first, second or third angle and a corresponding second mode second threshold for the first, second or third angle, the range of values representing a specified third effect for the second true type of film, the output indicates that the film comprises the second true type.

Optionally, the method may further comprise: imaging the birefringence pattern of the film at a first angle and at least one of a second angle and/or a third angle; comparing an image of the birefringence pattern at the first, second or third angle with a corresponding image representing a predetermined birefringence pattern of the authentic polymer film at the corresponding first, second and third angles; and outputting an authenticity signal indicative of the authenticity or otherwise of the film based on the comparison.

Optionally, the method may further comprise: outputting data representing the imaged birefringence pattern from the imaging device to a processor; and comparing the output data with a data set representing a predetermined birefringence pattern.

Optionally, the method may further comprise: the film is illuminated using an emitter comprising a white light source.

Optionally, the method may further comprise: a photosensitive array is provided to perform the imaging step.

Optionally, the method may further comprise: modifying the first effect to introduce a predetermined amount of offset into a value or range of values representing the first effect as measured at the first angle and the second and/or third angles; and measuring the first effect as modified.

Optionally, the method may further comprise: communicating output signals from the first detector and/or optionally the second detector and/or the third detector to the processor; and comparing the value of the output signal representing the first effect as modified with a value or range of values representing a specified first effect corresponding to a predetermined birefringence characteristic of an authentic polymer film and as modified by the same optical response modifier.

According to another aspect of the present invention there is provided a computer program comprising computer program elements operable in a computer processor to implement one or more aspects of an authentication apparatus as described above and below.

According to another aspect of the present invention, there is provided a computer program comprising computer program elements operable in a computer processor to implement one or more aspects of the method as described above and below.

According to another aspect of the invention, there is provided a computer readable medium carrying a computer program as described above.

One or more specific embodiments according to aspects of the present invention will be described, by way of example only, and with reference to the following drawings.

FIGS. 1 to 3 schematically illustrate components of a known apparatus for implementing different methods of observing birefringence;

figures 4a to 4d schematically illustrate perspective, top plan, side and end views of an authentication device according to one or more embodiments of the present invention;

FIG. 5 schematically illustrates a perspective view of the authentication device of FIGS. 4a through 4d in an optional arrangement;

FIG. 6 schematically illustrates a perspective view of the authentication device of FIGS. 4a through 4d in another optional arrangement;

figures 7a and 7b schematically illustrate perspective views of another authentication device according to one or more embodiments of the present invention;

FIG. 8 schematically illustrates a perspective view of a further authentication device in accordance with one or more embodiments of the invention;

FIG. 9 schematically illustrates a perspective view of yet another authentication device in accordance with one or more embodiments of the invention;

FIG. 10 schematically illustrates a perspective view of yet another authentication device in accordance with one or more embodiments of the invention;

FIG. 11 illustrates a graph of birefringence versus percent transmission for a 60 μm BOPP film; and

FIG. 12 illustrates a Michel-Levy graph;

FIG. 13 schematically illustrates a perspective view of an optional arrangement of the apparatus illustrated in FIG. 10;

FIG. 14 illustrates a graph of delay versus intensity as measured by the detector of the device of FIG. 13 when operating in a first mode;

FIG. 15 illustrates a plot of delay versus intensity as measured by the detector of the device of FIG. 13 when operating in a second mode; and

fig. 16 illustrates a combined view of the views of fig. 14 and 15.

Fig. 4 a-4 b illustrate a verification device 100 comprising a birefringence measurement device 102, a processor 104 and an alarm system 106.

The verification device 100 is operable to measure a birefringence characteristic of an item 108 (e.g., a banknote). In particular, the authentication device 100 is operable to measure the birefringence of an item 108 positioned in a measurement region of the authentication device 100.

A processor 104 (optionally a microprocessor) is operable to control the birefringence measurement device 102. An input of birefringence measurement device 102 is coupled to processor 104 and is controllable by processor 104. An output of birefringence measurement device 102 is coupled to processor 104. The processor 104 is operable to determine whether the item 108 in the verification device is genuine based on the output signals received from the birefringence measurement device 102. The results of such determinations are indicated (e.g., to an equipment operator) via the alarm system 106. The alarm system 106 is coupled to the processor 104 and is operable to output an indication of authenticity or otherwise based on signals received from the processor 104.

Birefringence measurement device 102 includes an emitter 110 (optionally, an LED), a first polarizer 112, a second polarizer 114, and a detector 116 (optionally, a photodiode). The polarizers 112, 114 are spaced apart and oriented so as to be substantially parallel. The area between the polarizers 112, 114 defines the measurement area.

The elements of birefringence measurement device 102 are arranged such that emitter 110 and first polarizer 112 are positioned on a first side of the measurement zone of birefringence measurement device 102, and first detector 116 and second polarizer 114 are positioned on a second side of the measurement zone (i.e., opposite first emitter 110 and first polarizer 112).

The emitter 110 is operable to illuminate the first polarizer 112 with electromagnetic radiation (represented in the figure by arrow IL). This illumination electromagnetic radiation IL is polarized by the first polarizer 112 as it passes through the first polarizer 112 and proceeds as polarized illumination electromagnetic radiation (represented by arrow PIL in the figure) to illuminate a portion of the article 108 positioned in the measurement area. The polarized illumination transmitted through a portion of the article 108 proceeds with a portion of the electromagnetic radiation (represented by arrow TL) toward the second polarizer 114. This transmitted electromagnetic radiation TL is polarized by the second polarizer 114 as it passes through the second polarizer 114 and proceeds towards the detector 116 as polarized transmitted electromagnetic radiation (represented by arrows PTL1, PTL2, PTL 3). The detector 116 is positioned, oriented, and operable to receive polarized transmitted electromagnetic radiation PTL1, PTL2, or PTL 3.

The measurement region generally defines a plane between the spaced polarizers 112, 114. The first polarizer 112 is spaced from this first plane and is positioned in a second plane located on a first "upstream" side of the measurement region. The second plane is substantially parallel to the first plane. Similarly, the second polarizer 114 is spaced from the first plane and positioned in a third plane located on a second "downstream" side of the measurement region. Which is positioned opposite the first polarizer 112 and the third plane is substantially parallel to the first and second planes. The arrangement of the transmissive orientations of the first polarizer 112 and the second polarizer 114 is such that they comprise crossed polarizers. That is, the first polarizer 112 is arranged such that its transmission orientation is about +45 ° from the transmission orientation of the portion of the item 108 positioned in the measurement region. The second polarizer 114 is arranged such that its transmission orientation is about-45 ° to the transmission orientation of the portion of the article 108 positioned in the measurement region. Alternatively, the transmission orientation of the first polarizer 112 may be such that it is about-45 ° to the transmission orientation of the portion of the item 108 positioned in the measurement region, and the transmission orientation of the second polarizer 114 may be such that it is about +45 ° to the transmission orientation of the portion of the item 108 positioned in the measurement region.

Thus, in the illustrated arrangement, the illuminating electromagnetic radiation IL emitted by the emitter 110 will be polarized by the first polarizer 112 and will illuminate the portion of the item 108 positioned in the measurement area as polarized illuminating electromagnetic radiation PIL. This polarized illumination electromagnetic radiation PIL passes through article 108 and proceeds as transmitted electromagnetic radiation TL to second polarizer 114 (i.e., a cross-polarizer). The transmitted electromagnetic radiation TL passes through the second polarizer 114 and proceeds as polarized transmitted electromagnetic radiation PTL1, PTL2, or PTL3 for reception by the detector 116. In response to detecting the polarized transmitted electromagnetic radiation incident thereon, PTL1 or PTL2 or PTL3, the detector 116 outputs a signal to the processor 104 that is proportional to the intensity of the polarized transmitted electromagnetic radiation, PTL1 or PTL2 or PTL3, respectively.

The detector 116 is mounted on a translation device (not shown). The translation device may be controlled by the processor 106 to alter the position of the detector 116 relative to the second polarizer 114. This may cause the detector 116 to measure the polarized transmitted electromagnetic radiation transmitted from the second polarizer 114 at different angles.

Such an arrangement is illustrated in fig. 4 a-4 d using a convention in which a detector is represented using a dashed line (and reference numeral 116') when positioned to receive polarized transmitted electromagnetic radiation transmitted from the second polarizer 114 at the first angle θ (i.e., polarized transmitted electromagnetic radiation transmitted by the polarizer 114 is represented by dashed arrow PTL 1). The detector is represented using a dashed line (and reference numeral 116 ") when positioned to receive the polarized transmitted electromagnetic radiation transmitted from the second polarizer 114 at the second angle Φ (i.e., the polarized transmitted electromagnetic radiation transmitted by the polarizer 114 is represented by the dashed arrow PTL 2). When the detector is positioned to receive polarized transmitted electromagnetic radiation transmitted from the second polarizer 114 at a third angle (i.e., the polarized transmitted electromagnetic radiation transmitted by the polarizer 114 is represented by the solid arrow PTL3), the detector is represented using a solid line (and reference numeral 116).

In the illustrated arrangement, the detector 116 is operable to measure the received polarized transmitted electromagnetic radiation transmitted from the second polarizer 114 at three different angles, namely: at a first angle θ (optionally, 45 °) perpendicular to the plane of the second polarizer 114; at a second angle Φ (optionally, 45 °) perpendicular to the plane of the second polarizer 114 in both the horizontal and vertical directions; and at a third angle normal to the plane of the second polarizer 114 (and thus normal to the plane of the film in the article 108). Thus, the detector 116 will output three measurement signals to the processor 104.

Upon receiving the three output measurement signals from the first detector 116, the processor 104 is operable to: comparing the value of a first one of the received signals with a first set of predefined values stored in a database (not shown); comparing the value of a second one of the received signals with a second set of predefined values stored in the database; and comparing the value of a third one of the received signals with a third set of predefined values stored in the database. These predefined values correspond to the values of polarized transmitted electromagnetic radiation expected when an authentic item (e.g., an authentic film) is positioned in the measurement region.

After performing the comparison, the processor 104 is operable to command the alarm system 106 to indicate that the film/article is authentic or non-authentic. If the result of the comparison is positive (i.e., the film is authentic), the processor is operable to send a signal to the alarm system 106 containing a command issuing an indication that the film/article is authentic. Otherwise, the processor is operable to send a signal to the alarm system 106 containing a command to issue an indication that the film/article is not authentic.

The authentication device 100 need not measure polarized transmitted electromagnetic radiation at all three angles in order to determine the authenticity of an item positioned therein. Indeed, in an optional arrangement, the verification device 100 may measure both angles as part of the verification exercise only.

When the polarized transmitted electromagnetic radiation transmitted from the second polarizer is measured at an angle normal to the plane of the film (PTL3), an article 108 comprising a highly oriented film will produce a high reading from detector 116 (because a large amount of electromagnetic radiation will be transmitted, i.e., the polarized transmitted electromagnetic radiation transmitted from the second polarizer (PTL3) will be relatively high). However, when the polarized transmitted electromagnetic radiation transmitted from the second polarizer is measured at an angle normal to the plane of the film (PTL3), the balanced film will produce a zero or low reading from detector 116 because the behavior of the electromagnetic radiation passing through the first and second crossed polarizers will be largely unchanged.

When the polarized transmitted electromagnetic radiation transmitted from the second polarizer is measured at an angle perpendicular to the film plane (PTL3), cast and bubble films (e.g., BOPP films) will produce a relatively low birefringence signal at the detector 116. On the other hand, when the tenter film is positioned in the measurement zone, when the polarized transmitted electromagnetic radiation transmitted from the second polarizer is measured at a perpendicular angle to the film plane (PTL3), the detector 116 will produce a high birefringence signal that will be different from the birefringence signals of the cast and bubble films. When the processor 104 compares the output signal from the detector 116 to a predefined value indicative of an authentic film (i.e., a value representing the birefringence of a particular film type that is deemed authentic), the processor 104 finds such a difference between the birefringence signal of the tentered film compared to the expected signal (in the case where the film is a bubble film). After performing the comparison, the processor 104 is operable to command the alarm system 106 to indicate that the film/article is not authentic.

For example, the apparatus may be suitable in the case where the genuine article comprises a substrate formed by a bubble process and the counterfeit article in general comprises a substrate formed by a tenter frame process. However, in instances where the authentic article comprises a substrate formed by a tentering process, further processing steps may be required in order to provide an indication as to whether the article with the tentered film substrate is authentic or otherwise.

When the polarized transmitted electromagnetic radiation transmitted from the second polarizer is measured at an angle normal to the film plane for cast or bubble films (PTL3), the difference in output signals from the detector 116 is relatively small. Therefore, when relying solely on the measurement of polarized transmitted electromagnetic radiation transmitted from the second polarizer at an angle perpendicular to the film plane (PTL3), the authentication device 100 may have difficulty distinguishing between the two types of films. In this example or in an alternative example where the measurement is taken from a non-perpendicular angle, the apparatus 100 may be operable to measure the polarized transmitted electromagnetic radiation transmitted from the second polarizer 114 at one or both of the first angle θ and the second angle Φ. When the detector 116 is positioned to receive polarized transmitted electromagnetic radiation transmitted from the second polarizer 114 at the first and/or second angles (PTL1, PTL2), the output signal from the detector 116 may be used by the processor 104 as a further parameter (or alternatively parameter) for a contrast process to determine the authenticity or other aspect of a film/article positioned in the measurement area.

Using planar geometry, it can be conveniently described that the detector 116 is positioned at several locations so as to receive the polarized transmitted electromagnetic radiation transmitted from the second polarizer 114 at different angles. A plane is defined as a surface perpendicular to the vector of coordinates [ xyz ]. A plane perpendicular to the vector (001) is defined as a (001) plane. Thus, in the arrangement described above and illustrated in fig. 4a to 4d, when detector 116 is positioned to measure the polarized transmitted electromagnetic radiation transmitted from the second polarizer (i.e., (PTL3)) at an angle normal to the film plane, its position relative to the film plane (assuming the film plane is the x-y plane) can be defined by the geometric direction described by vector (001). The detector 116 effectively observes the x-y plane of the film (i.e., the (001) plane) along the z-axis (i.e., defined by the vector (001)).

Similarly, for the case when the detector 116 is positioned to measure the polarized transmitted electromagnetic radiation transmitted from the second polarizer at a first angle θ (i.e., (PTL1)), the first angle θ may be 45 ° from the normal to the plane of the second polarizer 114. Using a planar geometric vector convention, the position of detector 116 relative to the plane of the membrane can be defined (in one example) by the geometric orientation described by vector (110). Thus, detector 116 observes the (110) plane of the film along the direction defined by vector (110).

For the case when the detector 116 is positioned to measure the polarized transmitted electromagnetic radiation transmitted from the second polarizer at the second angle Φ (i.e., (PTL2)), the second angle Φ may be 45 ° from the normal to the plane of the second polarizer 114 in both the horizontal and vertical directions. Using the planar geometry vector convention, the position of detector 116 relative to the plane of the membrane can be defined by the geometric orientation described by vector (111). Thus, detector 116 observes the (111) plane of the film along the direction defined by vector (111).

Measurements made at the first angle θ and the second angle Φ may be suitable to allow the apparatus 100 to distinguish between bubble films and cast films. Measurements made on such films at angles perpendicular to the plane of such films may be relatively similar, and thus further measurements made at first and second angles (when used by a processor for comparison) may be used to distinguish between the two types.

In an optional arrangement, the authentication device 100 may comprise a path along which the item may be transported. The measurement area forms part of this path. Thus, in this particular arrangement, the item may be transported along the path from one side of the authentication apparatus 100 to the other, and through the measurement region during its transport. That is, in this optional arrangement, the item to be authenticated may be moved relative to the authentication device 100, or vice versa. In another optional arrangement, the verification measurement may be made while the article is stationary. That is, the item may be introduced to an item location area (the measurement area forming part of) of the authentication device 100 where it is held until an authentication measurement has been made.

This apparatus 100 may be implemented, for example, in a banknote validation system.

The operation of the authentication apparatus 100 illustrated in fig. 4a to 4d may be summarized as follows. Birefringence measurements are performed on articles/films positioned in the measurement area. At least one birefringence measurement is performed using detector 116 at least one non-perpendicular angle relative to the film plane. The processor compares the value of the signal generated by the birefringence measurement to the value corresponding to the real film. If the measured value matches a value corresponding to an authentic film (or is within a suitable range of values considered authentic), the processor is operable to instruct the alarm system to provide an indication that the film is authentic. However, if one of the measurements (optionally two of the measurements; further optionally three of the measurements) does not match (or is outside of a suitable range of values considered to be authentic) the value (or values) corresponding to an authentic membrane, the processor is operable to instruct the alarm system to provide an indication that the membrane is not authentic.

Figure 5 illustrates an optional arrangement of the authentication apparatus 100 illustrated in figures 4a to 4d and described above.

The arrangement is similar to that illustrated in fig. 4 a-4 d and described above, except that the movable detector 116 is replaced with two fixed detectors 116a, 116 b. First stationary detector 116a is positioned to receive polarized transmitted electromagnetic radiation transmitted from second polarizer 114 at a first angle θ (represented by arrow PTL 1). Second stationary detector 116b is positioned to receive polarized transmitted electromagnetic radiation transmitted from second polarizer 114 at a second angle (represented by arrow PTL 2).

In this arrangement, the first and second stationary detectors 116a, 116b may simultaneously measure respective portions of the polarized transmitted electromagnetic radiation transmitted from the second polarizer 114 (i.e., PTL1, PTL 2).

Upon receiving the output measurement signals from the first stationary detector 116a and the second stationary detector 116b, the processor 104 is operable to: comparing the value of the signal received from the first stationary detector 116a to a first set of predefined values stored in a database (not shown); and comparing the values of the signal received from the second stationary detector 116b to a second set of predefined values stored in the database. These predefined values correspond to the values of polarized transmitted electromagnetic radiation expected when an authentic item (e.g., an authentic film) is positioned in the measurement region.

Fig. 6 illustrates yet another optional arrangement of the authentication apparatus 100 illustrated in fig. 4 a-4 d and described above.

The arrangement is similar to that illustrated in fig. 5, except that three fixed detectors (116a, 116b, 116c) are employed instead of two fixed detectors. First stationary detector 116a is positioned to receive polarized transmitted electromagnetic radiation transmitted from second polarizer 114 at a first angle θ (represented by arrow PTL 1). Second fixed detector 116b is positioned to receive polarized transmitted electromagnetic radiation transmitted from second polarizer 114 at second angle Φ (represented by arrow PTL 2). Third stationary detector 116c is positioned to receive polarized transmitted electromagnetic radiation transmitted from second polarizer 114 at a third angle (represented by arrow PTL3)

In this arrangement, the first, second, and third fixed detectors 116a, 116b, 116c may simultaneously measure respective portions of the polarized transmitted electromagnetic radiation transmitted from the second polarizer 114 (i.e., PTL1, PTL2, PTL 3).

Upon receiving the output measurement signals from the first, second, and third stationary detectors 116a, 116b, 116c, the processor 104 is operable to: comparing the value of the signal received from the first stationary detector 116a to a first set of predefined values stored in a database (not shown); comparing the values of the signal received from the second stationary detector 116b to a second set of predefined values stored in the database; and comparing the value of the signal received from the third stationary detector 116c to a third set of predefined values stored in the database. As previously mentioned, these predefined values correspond to expected values of polarized transmitted electromagnetic radiation when an authentic item (e.g., an authentic film) is positioned in the measurement region.

As described above, after performing the comparison, the processor 104 is operable to command the alarm system 106 to indicate that the film/article is authentic or non-authentic. If the result of the comparison is positive (i.e., the film is authentic), the processor is operable to send a signal to the alarm system 106 containing a command issuing an indication that the film/article is authentic. Otherwise, the processor is operable to send a signal to the alarm system 106 containing a command to issue an indication that the film/article is not authentic.

In either optional arrangement, the authentication apparatus 100 may employ an arrangement of both fixed and movable detectors, and/or may be arranged to measure polarized transmitted electromagnetic radiation transmitted from the second polarizer 114 at four or more angles.

Fig. 7a and 7b illustrate another authentication device in accordance with one or more embodiments of the present invention.

Features similar to those illustrated in fig. 4 a-4 d, 5 or 6 are also illustrated in fig. 7a and 7 b. In fig. 7a and 7b, reference numerals of type 2XX are used instead of 1XX to designate features common to those of fig. 4a to 4d, 5 or 6. Thus, in fig. 7a and 7b, the authentication device is denoted by reference numeral 200 (instead of 100), the birefringence measurement device is denoted by reference numeral 202 (instead of 102), and so on.

The authentication apparatus 200 illustrated in fig. 7a and 7b differs from the authentication apparatus 100 described previously (and as illustrated in fig. 4a to 4d, 5 or 6) in that: the second polarizer 214 may be rotated between a polarizing orientation (as illustrated in fig. 7 a) and a non-polarizing or perpendicular transmission orientation (as illustrated in fig. 7 b). When oriented in the polarization orientation, the second polarizer 214 functions in the same manner as the second polarizer 114 as previously described. That is, the transmission orientation of the second polarizer 214 is perpendicular to the transmission orientation of the first polarizer 212, such that the first and second polarizers 212, 214 comprise crossed polarizers. Thus, and as with the previously described arrangement of the transmission orientations of the first and second polarizers 112, 114, the first polarizer 212 is arranged such that its transmission orientation is about +45 ° to that of the portion of the item 208 positioned in the measurement region. The second polarizer 214 (in the polarization orientation) is arranged such that its transmission orientation is about-45 ° to the transmission orientation of the portion of the item 208 positioned in the measurement area. Alternatively, the transmission orientation of the first polarizer 212 may be such that it is about-45 ° to the transmission orientation of the portion of the item 208 positioned in the measurement region, and the transmission orientation of the second polarizer 214 may be such that it is about +45 ° to the transmission orientation of the portion of the item 208 positioned in the measurement region.

When oriented in the unpolarized orientation, the transmission orientation of the second polarizer 214 is the same as the transmission orientation of the first polarizer 212 (i.e., it is parallel to the transmission orientation of the first polarizer 212). In this example, the first polarizer 212 and the second polarizer 214 are arranged such that their transmission orientations are about +45 ° from the transmission orientation of the portion of the item 208 positioned in the measurement region. Alternatively, the transmission orientation of the first and second polarizers 212, 214 may be such that it is about-45 ° from the transmission orientation of the portion of the article 208 positioned in the measurement region.

The authentication device 200 comprises an actuator (not shown) operable to effect rotation of the second polarizer 214 from a polarizing orientation to a non-polarizing orientation, and vice versa. The processor 204 is operable to control the actuator.

In operation, the detector 216 is operable to measure the received polarized transmitted electromagnetic radiation (represented by arrow PTL in FIG. 7 a) transmitted from the second polarizer 214 when the second polarizer 214 is oriented in a polarization orientation. The first measurement signal is communicated to the processor 204.

The detector 216 is further operable to measure the received transmitted electromagnetic radiation (represented by arrow TL in fig. 7 b) transmitted from the second polarizer 214 when the second polarizer is oriented in a non-polarizing orientation. The second measurement signal is communicated to the processor 204.

Upon receiving the first and second measurement signals from the detector 216, the processor 204 is operable to: comparing the values of the received first measurement signal with a first set of predefined values stored in a database (not shown); and/or comparing the value of the received second measurement signal with a second set of predefined values stored in a database. The first set of predefined values corresponds to expected values of polarized transmitted electromagnetic radiation when an authentic item (e.g., an authentic film) is positioned in the measurement region. The second set of predefined values corresponds to values of directly transmitted electromagnetic radiation expected when the genuine article/film is positioned in the measurement area (e.g., values indicative of the intensity of electromagnetic radiation directly transmitted by the genuine article/film).

In an optional arrangement, the processor 204 may be operable to subtract the value of the received second measurement signal from a predefined value indicating the absence of an item/film positioned in the measurement region. The processor 204 is then operable to compare the subtracted value with a second, different set of predefined values corresponding to the expected value of transmitted electromagnetic radiation (birefringence value) when the genuine article/film is positioned in the measurement area.

In this optional arrangement, the intensity of electromagnetic radiation transmitted by the article/film 208 to the detector 216 has the value of I with the second polarizer 214 in the unpolarized orientation_NP. If no item/film 208 is present in the measurement area, the illumination radiation passes only through the air in the measurement area, and the intensity of the electromagnetic radiation received at detector 216 with polarizer 214 in the unpolarized orientation has the value I_AIR. In order to obtain the above-mentioned value (I)_RV) From the intensity values I_AIRSubtracting the intensity value I_NP. Thus, I_AIR-I_NP＝I_RV. The value obtained I_RVEffectively a measure of the birefringence of the film. The processor 204 will do thisThe value obtained I_RVCompared to a second, different set of predefined values, thereby allowing the processor 204 to make a verification determination.

As has been described previously, in an arrangement comprising two crossed polarizers with a birefringent material positioned therebetween, the birefringence is produced by interference caused by recombination of the ordinary and extraordinary rays upon transmission by the second crossed polarizer. Birefringent electromagnetic radiation is structured to be of one polarization and pass through a second polarizer, while the remainder is structured with the opposite polarization and is reflected or absorbed by the second polarizer. Non-transmissive electromagnetic radiation may be transmitted if the second polarizer is rotated such that it is parallel to the first polarizer and not crossed by it. This effect is employed in the above arrangement.

Films or articles comprising films having relatively low levels of birefringence are indistinguishable from air and may not be visible near the printing environment in the case of crossed polarizers. The arrangements described previously and later rely on the phenomenon that birefringence effectively redirects electromagnetic radiation and uses crossed polarizers to view the electromagnetic radiation to allow one portion of the redirected radiation to be observed. When the polarizers are parallel, another portion (i.e., the "non-transmissive" portion referred to above) can be seen. The behavior of devices employing parallel polarizers is that high intensity electromagnetic radiation is transmitted and the intensity of this electromagnetic radiation will decrease with birefringence (e.g., when a birefringent film is introduced into the device between the polarizers). In this parallel polarizer example, an empty device would result in a high intensity of electromagnetic radiation being received at the detector, while a film positioned in the measurement area of the device would result in a lower intensity of electromagnetic radiation being received at the detector. The difference between the measurement of electromagnetic radiation of high intensity (the device is empty) and the measurement of electromagnetic radiation of slightly lower intensity (the film is present) provides a measure of the birefringence of the film.

Accordingly, the authentication apparatus 200 described above and as illustrated in fig. 7a and 7b may be adapted to determine the authenticity of films exhibiting relatively low levels of birefringence. In factSince highly oriented films, such as, for example, BOPP films, have a relatively low level of birefringence (which may be zero in some instances), any "measurement" of this property using an apparatus in which the polarizers are in a crossed configuration may give results that may be difficult to distinguish from background noise. Measurements made using an apparatus in which the polarizers are not in a crossed configuration may allow measurements representing "inverse" birefringence (i.e., the intensity (I) of electromagnetic radiation received when the apparatus is empty to be made_AIR) Subtracting the intensity (I) of the electromagnetic radiation received when the membrane is positioned in the measurement area of the apparatus_NP) Is equal to I_RVAnd I is_RVProportional to the "inverse" birefringence of the film (i.e., film transmission).

In the above arrangement (and optional arrangement), after performing the comparison, the processor 204 is operable to command the alarm system 206 to indicate that the film/article is authentic or non-authentic. If the result of the comparison is positive (i.e., the film is authentic), the processor is operable to send a signal to the alarm system 206 containing a command issuing an indication that the film/article is authentic. Otherwise, the processor is operable to send a signal to the alarm system 206 containing a command to issue an indication that the film/article is not authentic.

This arrangement may also be suitable for apparatus operable to determine the authenticity of a banknote having a polymer film substrate and wherein the authenticity measurement is carried out on a "window" region of the banknote (i.e. a region of the banknote where the film substrate is exposed), e.g. where no printing overlies the region or where no disclosed security feature overlies the region. As will be appreciated, the banknote becomes worn over time, and one worn aspect of the banknote can damage the window area that manifests itself as a banknote. Such damage may include, for example, scratching of the window surface and/or transfer of greasy substances to the window surface, which can result in a window having a hazy appearance. These types of "damage" can effectively physically prevent (or partially prevent) the transmission of light through the window area of the banknote. This may affect the measurements made during the verification process.

In the arrangements described above with respect to fig. 7a and 7b, physical blockage (e.g. via damage) of the window region of the banknote can be observed as an effective reduction in birefringence in the cross-polariser mode of operation. However, physical blockage of the window area of the banknote is observable in the non-cross-polarized mode of operation as an effective increase in birefringence. In both cases, the physical blockage does not alter the birefringence of the film substrate itself, but rather affects the measurement made by the detector and is therefore perceived as a refractive index different from what is actually done.

By using intensity values obtained in the crossed polarizer mode of operation (i.e., polarized mode) and the non-crossed polarizer mode of operation (i.e., unpolarized mode), a more accurate measurement of birefringence of the damaged/blurred film may be obtained. As described above, the intensity of electromagnetic radiation received at the detector when the second polarizer is in a non-polarizing orientation (i.e., a non-crossed polarizer mode of operation) is represented by I_NPTo indicate. The intensity of the electromagnetic radiation received at the detector when the second polarizer is in the polarization orientation (i.e., cross-polarizer mode of operation) is represented by I_PTo indicate. To determine a measure of the intensity, and thus the birefringence of the film, that can be expected without damaging (or obscuring) the window area of the film, the difference between the two intensity values can be obtained and this difference can then be halved. Or from I_NPSubtracting the result, or adding the result to I_PTo obtain a more accurate measurement of the birefringence of the film (I)_{Is not damaged}(I_UNDAMAGED)). Namely, it is

(I_NP–I_P)/2+I_P＝I_{Is not damaged}

Or

I_NP–(I_NP–I_P)/2＝I_{Is not damaged}

Processor 204 may represent this birefringence by a value (i.e., I)_{Is not damaged}) Compared to a predefined value to determine authenticity.

FIG. 8 illustrates another authentication device in accordance with one or more embodiments of the present invention.

Again, features similar to those illustrated in fig. 4 a-4 d, 5, 6, 7a or 7b are also illustrated in fig. 8. In fig. 8, features common to those of fig. 4a to 4d, fig. 5, fig. 6, fig. 7a or fig. 7b are designated using reference numerals of type 3XX instead of 1XX or 2 XX. Thus, in FIG. 8, the authentication device is represented by reference numeral 300 (instead of 100 or 200), the birefringence measurement device is represented by reference numeral 302 (instead of 102 or 202), and so on.

The authentication apparatus 300 illustrated in fig. 8 differs from the authentication apparatus 100 described previously (and as illustrated in fig. 4 a-4 d) in that: the detector 116 is replaced by an imaging array 320 (e.g., a photosensitive array) (or, in an optional arrangement not illustrated, supplemented by an imaging array 320 (e.g., a photosensitive array)).

As with the previously described arrangement of the transmission orientations of the first and second polarizers 112, 114, the first polarizer 312 is arranged such that its transmission orientation is about +45 ° from the transmission orientation of the portion of the article 308 positioned in the measurement region. The second polarizer 314 (in the polarization orientation) is arranged such that its transmission orientation is about-45 ° to the transmission orientation of the portion of the article 308 positioned in the measurement region. Alternatively, the transmission orientation of the first polarizer 312 may be such that it is about-45 ° to the transmission orientation of the portion of the article 308 positioned in the measurement region, and the transmission orientation of the second polarizer 314 may be such that it is about +45 ° to the transmission orientation of the portion of the article 308 positioned in the measurement region.

Imaging array 320 is operable to image at least a portion of the film as viewed from the location of imaging array 320 via second polarizer 314. That is, imaging array 320 is positioned to receive polarized transmitted electromagnetic radiation (represented by arrow PTL in FIG. 8) transmitted from second polarizer 314. Imaging array 320 (alone or in conjunction with processor 304) may be operable to compile an image of a particular portion or area of the film of article 308 from polarized transmitted electromagnetic radiation transmitted from second polarizer 314 and received by imaging array 320.

The processor 304 is operable to compare the dataset corresponding to the compiled image with a dataset of predefined values stored in a database (not shown). The predefined value dataset corresponds to an expected image that will be observed when a real object (e.g., a real film) is positioned in the measurement region.

After performing the comparison, the processor 304 is operable to command the alarm system 306 to indicate that the film/article is authentic or non-authentic. If the result of the comparison is positive (i.e., the compiled image dataset matches the predefined value dataset corresponding to the expected image of the authentic film/article), then the film is deemed authentic and the processor is operable to send a signal to the alarm system 306 containing a command issuing an indication that the film/article is authentic. Otherwise, the processor is operable to send a signal to the alarm system 306 containing a command to issue an indication that the film/article is not authentic.

The authentication method implemented by the apparatus 300 of this arrangement may be suitable for implementing regional viewing of the film/article rather than point viewing as implemented by other arrangements described above. Employing such a "field observation" technique may allow the film to be validated based on its intrinsic birefringence pattern, which will be observable using the apparatus 300 of fig. 8. Thus, the birefringence pattern (if present) will be captured in the compiled image, and this observed birefringence pattern can be compared to the predefined image (i.e., the birefringence pattern) that would be expected to be observed if a real film were present in the apparatus 300.

In an optional arrangement of one or more of the embodiments described above and as illustrated in fig. 8, the emitter 310 can comprise a white light source (e.g., a light box) and/or the imaging array 320 can comprise a CCD camera. In another optional arrangement, the imaging array 320 may comprise a flatbed scanner.

FIG. 9 illustrates another authentication device in accordance with one or more embodiments of the present invention.

Again, features similar to those illustrated in the previous figures are also illustrated in fig. 9. In fig. 9, reference numerals of type 4XX, rather than 1XX, 2XX or 3XX, are used to designate features that have commonality with features of the previous figures. Thus, in fig. 9, the authentication device is denoted by reference numeral 400 (instead of 100, 200, or 300), the birefringence measurement device is denoted by reference numeral 402 (instead of 102, 202, or 302), and so on.

The authentication apparatus 400 illustrated in fig. 9 differs from the authentication apparatus previously described (and as illustrated in fig. 4 a-4 d, 5, 6) in that there is a single fixed detector 414, and in that it further comprises an optical response modifier 418.

An optical response modifier 418 is positioned (as with the first polarizer 412, the second polarizer 414, and the item 408) in the beam path of the electromagnetic radiation between the emitter 410 and the detector 416.

The optical response modifier 418 is operable to modify an observable optical response of the item 408 positioned in the measurement region. The modifying effect of the optical response modifier 418 is to modify the observed birefringence characteristic of the article 408 positioned in the measurement region. An optical response modifier 418 is provided to effectively introduce a predetermined amount of offset to a value representative of the intensity of the polarized transmitted electromagnetic radiation as received at detector 416 and as measured by detector 416.

The optical response modifier 418 optionally comprises a material suitable to act as a half-wave or quarter-wave retardation plate. The optical response modifier 418 (e.g., a birefringent material) controls the response by providing additive or subtractive retardation, which can be further modified by rotating the optical response modifier 418 relative to the rotation of the article 408 to line. The degree of change in delay can be calculated using the following equation:

Δr＝lΔncos(2θ)

where r is the retardation change, Δ n is the birefringence of the optical response modifier 418, l is the thickness of the optical response modifier 418 and θ is the angle of rotation relative to the measured angle of the article 408.

Thus, in operation, transmitted electromagnetic radiation TL transmitted by the article 408 is polarized by the second polarizer 414 as it passes through the second polarizer 414, and a portion of the transmitted electromagnetic radiation TL transmitted by the article 408 proceeds as polarized transmitted electromagnetic radiation (represented by arrow PTL) toward the detector 416. Before reaching detector 416, the polarized transmitted electromagnetic radiation PTL is incident on optical response modifier 418. A portion of the incident polarized transmitted electromagnetic radiation PTL is not transmitted (e.g., reflected or absorbed) and the remaining portion is transmitted by the optical response modifier 418. This remaining portion (hereinafter "optically modified transmitted radiation" OMTL) proceeds to and is received at detector 416.

In response to detecting the optically modified transmitted radiation OMTL incident on the detector 416, the detector 416 outputs a signal proportional to the intensity of the optically modified transmitted radiation OMTL to the processor 404.

Upon receiving the output measurement signal from detector 416, processor 404 is operable to: the value of the received signal is compared to a set of predefined values stored in a database (not shown). These predefined values correspond to the optically modified transmission radiation OMTL values expected when a real object (e.g. a real film) is positioned in the measurement area.

After performing the comparison, the processor 404 is operable to command the alarm system 406 to indicate that the film/article is authentic or non-authentic. If the result of the comparison is positive (i.e., the film is authentic), the processor is operable to send a signal to the alarm system 406 containing a command issuing an indication that the film/article is authentic. Otherwise, the processor is operable to send a signal to the alarm system 406 containing a command to issue an indication that the film/article is not authentic.

In prior art systems, birefringence is measured using equipment with a white light emitter and then integrating (essentially averaging) the intensity of light received at the detector. That is, measurements across the white spectrum are integrated. This means that measurements made for tenter films can be very similar to measurements made for BOPP bubble process films, where the manufacturing process control for those films is poor.

Measurements of birefringence have been normalized using a scale of 0 to 1, where a value of 0 indicates no birefringence (i.e., a pair of crossed polarizers, no article present). The value 1 represents the birefringence when an article with "half-wave" properties (retardation of about 275 nm) is present. In the standardized (i.e., 0 to 1) birefringence measurement scale used with previous measurement systems, BOPP bubble process films will typically produce a measurement reading of about 0.3 in the standardized birefringence measurement scale. However, a measurement reading of about 0.4 to about 0.6 in the normalized birefringence measurement scale can generally be seen for tenter films.

In an optional arrangement, the optical response modifier 418 can be controllably rotated by the processor 404 and an actuator (not shown) to alter the orientation of the x and y birefringence axes of the optical response modifier 418.

Since birefringence is additive, it is possible to change the zero point of the normalized birefringence measurement scale by either adding positive birefringence or subtracting negative birefringence. Thus, two films with the same birefringence will add up to produce twice as much retardation (and thus twice as much birefringence). When oriented at 90 ° with respect to each other, the same two films will effectively cancel each other out.

If an optical response modifier 418 (e.g., a film) is provided having a monochromatic birefringence of 0.3 in an axis opposite to the axis of the article being instrumented, the measurement of the optically modified transmitted radiation OMTL received at the detector 416 would be 0.3 when no article is present in the measurement area. When the measurement of the optically modified transmitted radiation OMTL received at detector 416 will be 0, the sample is placed so that the delay in the relative axis increases, which will decrease this value until the sample (i.e. the inserted article) birefringence is 0.3. Further increasing the delay in the relative axes will increase the measurement of the optically modified transmitted radiation OMTL received at detector 416. Using this technique means that the birefringence from 0 to 0.6 effectively becomes halved to 0.3.

The result of using the above technique for white light systems is a wider gap between the detector measurements for BOPP bubble process films (at the high end of the expected value for this type of film) and the detector measurements for tenter films (at the low end of the expected value for this type of film).

The arrangement of fig. 9 as described above may be suitable to help enable distinction between tenter films and BOPP bubble process films themselves having birefringence values in a similar range to that of BOPP bubble process films. Thus, the apparatus may be adapted to identify genuine bubble process films, genuine non-bubble process films (e.g. genuine films made using a tenter frame process) or non-genuine non-bubble process films.

FIG. 10 illustrates another authentication device in accordance with one or more embodiments of the present invention.

Again, features similar to those illustrated in the previous figures are also illustrated in fig. 10. In fig. 10, reference numerals of type 5XX, rather than 1XX, 2XX, 3XX or 4XX, are used to designate features that have in common with features of the previous figures. Thus, in FIG. 10, the authentication device is represented by reference numeral 500 (instead of 100, 200, 300, or 400), the birefringence measurement device is represented by reference numeral 502 (instead of 102, 202, 302, or 402), and so forth.

Before describing the authentication device 500 of fig. 10 in more detail, a birefringence measurement system as disclosed in WO2009/133390 will be described as background information.

The system disclosed in WO2009/133390 comprises an emitter- > a first polarizer- > a second (cross) polarizer- > a detector system, wherein the film to be authenticated is positioned between the first and second polarizers.

The emitter of the system is operable to emit white light. Such white light passing through the system comprises electromagnetic radiation of more than one wavelength but a certain complete wavelength range. Each wavelength in the range will interfere differently at the second polarizer according to its relationship to its wavelength. Equation (3) can be used to calculate the phase difference p, which describes the relationship between wavelength λ and retardation:

the amplitude a of the waveform formed by interference of two wavelengths with a phase difference p can be calculated by using equation (4):

for any ray of transmitted light, the intensity I can be calculated using equation (5):

equation (5) allows the intensity of the wave at a particular wavelength to be calculated and can be used to construct a spectrum showing how transmitted light will appear. However, it is the overall intensity T of the transmitted light across the range to be measured, and therefore this equation (5) must be modified to equation (6) as follows:

FIG. 11 shows the results of equation (6) as calculated for a 60 μm film in the range of 0 to 0.05 birefringence. As indicated previously, fig. 11 shows the transmitted intensity versus birefringence level of the film. As can be seen, a peak is reached, followed by a drop in oscillation intensity and a rise in oscillation intensity. FIG. 11 illustrates the phenomenon that an integrated detector will see; films with a birefringence several times that which is possible with films produced by the bubble process will have transmission values as small as 30% according to this scale, such as the region represented by box a (which is modeled and therefore may not be accurate in intensity). As can be appreciated, these transmission values are similar to the transmission values at the upper end of the range of transmission values (represented by box B) for films produced by the bubble process.

Birefringence is typically identified by reading from a Michel-Levy chart (illustrated herein in black and white only in fig. 12). The bottom x-axis is the retardation (mm) and is divided into different orders depending on its behavior. The first half of the first order (0 to 300nm) consists of a black to white transition, representing zero transmission to a white broadband. This first order corresponds to the first peak (0-0.004) in the graph illustrated in fig. 11. It should be noted that after the first half of the first order, the intensity falls to a value of significantly 30% of the maximum. This corresponds to the end of the first order and can be measured in practice by using a full wave membrane. The measured value is different from the calculated value (closer to 50% of the maximum value), possibly due to the simplification of the model defined by the above equation and the variation of the actual equipment.

A white light single detector integrated system of the type disclosed in WO2009/133390 enables measurements at the detector end of the system, which is actually a synthesis of the transmission of all light from a white light source into a single value. Thus, the color variations found at delays above the first order cannot be accounted for (see the full-color version of the Michel-Levy diagram illustrated at fig. 12 for more detail). Therefore, some information is lost in the measurements made by this type of system.

For further explanation, reference is again made to fig. 11. The transmission levels shown in fig. 11 may be mapped to the Michel-Levy diagram illustrated in fig. 12. The first period illustrated in fig. 11 corresponds to the first order black-to-white transition of the Michel-Levy diagram. The intermediate periods illustrated in fig. 11 correspond to the color bands at the higher order of the Michel-Levy chart illustrated in fig. 12 (shown only in black and white in fig. 12). If a full-color Michel-Levy diagram is referenced, then it can be seen that the color is transmitted at higher orders.

If a Michel-Levy chart is obtained and converted to gray scale and then the intensity lines across it are obtained, the resulting contour will have substantially the same shape as illustrated in fig. 1.

As can be seen in fig. 11, the film with birefringence at 0.01 (represented by point P) on this graph has approximately the same overall transmission value as the film at 0.002 (represented by Q), and still (as can be seen by cross-referencing the Michel-Levy diagram of fig. 12) has a five-fold retardation.

The relationship between blister and tenter films is even more extreme. The 60 μm tentered film will have a retardation value between 800 and 1200 while the bubble film will have a retardation value of less than about 200. However, converting these values into the graph of FIG. 11 yields a transmission that is approximately similar to about 40% (200nm retardation (Michel-Levy plot) corresponds to a birefringence of about 0.002 to 0.003 in FIG. 11; 800 to 1000nm retardation corresponds to a birefringence of about 0.015 to 0.025 in FIG. 11).

Thus, this measurement technique returns a similar value representing the birefringence of very different films. The reason for the transmission level is very different. The blister film will have a nearly flat spectrum which appears white to the observer's eye, and the tentered film will transmit a particular color, with the result that part of the visible spectrum will be lost. This loss of part of the visible spectrum is the cause of the reduction of the overall intensity.

Measurements that allow distinguishing wavelengths will reveal this difference. The arrangement of fig. 10 is operable to employ such techniques in an attempt to avoid such loss of information as referenced above. In addition, the arrangement of FIG. 10 is designed to fit color information that can be transmitted (i.e., corresponding to a higher order of the Michel-Levy chart). To do so, the arrangement of FIG. 10 may employ a 1 to 20 scale that describes the higher order of birefringence, to supplement the 0 to 1 scale referenced above. Such a level may be employed by the processor when the processor is operative to implement a process for converting the spectrum into single values (described in more detail later). In general, the process allows wavelength information (essentially "color" information) to be kept in any measurement and effectively adds the variance of a set of measured intensity values to the values themselves.

The "color" measurement, which may be performed by a process in the processor 504, may reduce the sensitivity of the system to misaligned samples. For example, a highly birefringent tenter film will transmit light in the red portion of the visible electromagnetic spectrum. That is, the detector will receive electromagnetic radiation at a wavelength corresponding to the red portion of the electromagnetic spectrum. The tenter film will still transmit red light as it rotates, but the measured intensity will decrease as the film rotates. This reduction in intensity as the film rotates will be interpreted by a white light single detector integrated system as a reduction in birefringence. This is not the case with the color measurement system. The birefringence/retardation remains the same as the film rotates, but the amount of delayed light transmitted is reduced. This is due to two independent effects. For films that are delayed to the first order (refer to full-color Michel-Levy diagrams), where the transmission is actually black- > grey- > white, this is not evident for films that transmit red light: if the degree of delay changes, the observed color will change. However, it does not change and the observed intensity of red will only decrease. The color measurement system registers an overall reduced but consistent spectral shape of intensity.

Using the validation apparatus of fig. 10, a "red" 1000nm retardation film (i.e., a film that transmits red light) that has been inserted into the measurement region so as to be in misalignment will still be detectable as a non-bubble film (i.e., a relatively higher birefringence film), even if it is very out of alignment and the level of transmission is lower. This is because the use of the "line shape" determination process performed by the averaging module in the processor 504 (and discussed further later) places more emphasis on its flatness than the average intensity of the line. Thus, a color measurement system as illustrated in FIG. 10 is capable of interpreting color information in addition to intensity information to avoid the loss of information that can occur in a white light single detector integrated system. The authentication determination may be made by the processor 504 in this arrangement based on two sets of information.

Recognizing the systematic limitations of determining authenticity based on measuring birefringence under white light conditions, counterfeit money makers have only attempted to create counterfeit security documents in which the mechanical and lateral directions of a non-polymeric film substrate having a relatively high birefringence are tilted with respect to the edges of the substrate. That is, the machine and lateral directions of the substrate may not be parallel to the edges of the substrate. Thus, when this type of counterfeit security document is introduced into a system based on the measurement of birefringence using a white light emitter, single integrated detector technology to determine authenticity, the counterfeit security document may appear to the naked eye to be properly aligned. In practice, however, the machine and transverse directions of the substrate will be misaligned relative to the apparatus, and the effect that would be observed in the presence of a film substrate having a lower birefringence can be mimicked. That is, misalignment results in the observation of a birefringence that is lower than what would otherwise be observed if films with non-true, higher birefringence had been configured such that the machine and transverse directions were aligned.

The apparatus described above with respect to fig. 10 may be suitable for detecting a counterfeit security document formed on non-bubble process film substrates (i.e. those film substrates having relatively high birefringence, such as tenter frame films) in which the machine and transverse directions of the polymer film substrates are deliberately arranged so as not to be aligned when placed in the apparatus.

The authentication apparatus 500 illustrated in fig. 10 differs from some previously described authentication apparatuses in that there is a single fixed detector 514, and in that it further comprises at least one wavelength filtering element 518.

The at least one wavelength filtering element 518 is operable to be positioned in a beam path of electromagnetic radiation traveling between the emitter 510 and the detector 516.

In the illustrated arrangement, the wavelength filtering element 518 is operable to transmit a portion of the wavelengths of polarized transmitted electromagnetic radiation prior to reception by the detector 516. In an optional arrangement in which a plurality of wavelength filtering elements 518 are provided, each of the plurality of wavelength filtering elements 518 may function to transmit a different portion (i.e., a different wavelength range) of the spectrum of polarized transmitted electromagnetic radiation. Placement of one of the plurality of wavelength filtering elements 518 in the beam path may be accomplished by an actuator (not shown) controlled by the processor 504. In this optional arrangement, the apparatus may be operable to select different portions of the spectrum of polarized transmitted electromagnetic radiation, immediately prior to performing a detection measurement at detector 516.

Thus, in operation, transmitted electromagnetic radiation TL transmitted by the item 508 is polarized by the second polarizer 514 as it passes through the second polarizer 514, and a portion of the transmitted electromagnetic radiation TL transmitted by the item 508 proceeds as polarized transmitted electromagnetic radiation (represented by arrow PTL) toward the detector 516. Before reaching detector 516, polarized transmitted electromagnetic radiation PTL is incident on wavelength filtering element 518. Some wavelengths of the incident polarized transmitted electromagnetic radiation PTL are not transmitted (e.g., reflected or absorbed) and the remainder of the wavelengths are transmitted by the wavelength filtering element 518. This remaining portion (hereinafter "filtered transmitted radiation" FTL) proceeds to and is received at detector 516.

In response to detecting the filtered transmitted radiation FTL incident on the detector 516, the detector 516 outputs a signal proportional to the intensity of the filtered transmitted radiation FTL to the processor 504.

Processor 504 is operable to implement a process for converting spectra into single values. The process is described in more detail below. This single value is based on the average plus a factor describing the flatness of the spectrum. A flat spectrum will return a value approximately equal to the mean (or integrated intensity) of the spectrum: the blister will fall into this category. As the birefringence increases, the spectrum becomes tilted and eventually becomes much more complex, so the variance value increases partially and becomes dominant-thus, highly birefringent materials will obtain much larger values. A white light single detector integrated system of the type described above employs a 0 to 1 standardized measurement scale that will give readings of "0" (when the device is empty) and "1" (when the "half wave" membrane is positioned in the system). This roughly corresponds to the level on the graph of fig. 11.

To calibrate the verification device 500, an operator may perform a calibration process before starting the verification process.

A "dark" reading (i.e., a spectrum of an empty measurement region of the device with the transmitter 510 switched off) may be obtained. A "shallow" reading (i.e., a spectrum of the empty measurement region with the transmitter 510 turned on) is also obtained. The processor 504 is operable to flag the taking of measurements from these readings using a representation indicating that these readings are "dark" and "light" readings. The processor 503 is further operable to communicate the measurements to a suitable storage means for retrieval at some other point in time.

Once the calibration process is complete, the verification device 500 is ready to verify the sample.

When the sample article/film 508 is positioned in the measurement area of the authentication device 500, a sample reading is obtained (i.e., a spectrum of the measurement area with the sample positioned in the measurement area and the light turned on).

The processor operates on the range of measurements output by the detector 516 to the processor 504 to calculate the resulting spectrum. Processor 504 is operable to perform the following calculations to calculate a resulting spectrum:

the spectrum obtained is (sample reading-dark reading)/(light reading-dark reading)

The processor 504 is operable to "smooth" the calculated resulting spectrum using an averaging module (not shown). The procedure implemented by the averaging module is as follows:

temp [ j ] - (spectrum [ j-3] + spectrum [ j-2] + spectrum [ j-1] + resultSpectrum [ j ] + spectrum [ j +1] + spectrum [ j +2] + spectrum [ j +3 ]/7)

Such a "smoothing" function may reduce the effect of random noise on the sample variance.

Each result (temp [ j ]) is averaged such that there are +/-3 results on either side of the result in the entire spectrum.

The processor 504 is operable to use an averaging module to then calculate the mean of the spectrum and the statistical variance of the spectrum.

The processor 504 is then operable to calculate a polynomial for the first order (i.e., black to white) delay spectrum from the theoretical ideal shape (using the average of the actual spectrum to locate its intensity) using an averaging module.

The processor 504 is then operable to calculate the variance of this resulting spectrum from the general shape of the polynomial using an averaging module.

The processor 504 is operable to make the following decisions: if the variance is above a certain level, polynomial correction is applied. The reason for this is that for low levels of birefringence, the calculated spectral lines are tilted towards the red end of the spectrum. Correcting for this flattens the low birefringence lines, thereby reducing the effect of this tilt on the variance. However, if such a tilt is applied to the birefringence results near the end of the first order (see Michel-Levy charts), it can either reduce the final variance or unfairly increase the variance of the boundary film.

If the processor 504 determines that polynomial correction has been applied, it recalculates the variance of the flattened lines.

The calculated variance describes the flatness of the line (as described above). The flatter the line, the lower the variance. When all the low birefringence lines have been flattened according to a theoretical polynomial, the first order of birefringence will correspond to the average intensity. The formula is used to describe the line:

result is mean +100 variance

Using this technique, the results are extremely sensitive to variations in line flatness, with the following results:

0 to 0.8 is closely consistent with current white light single detector integrated system 0 to 1 (half wave plate) ratings.

0.8 to 1.2-the accuracy loss in this region when the line starts to tilt, corresponding roughly to 0.8 to 1 on the scale of 0 to 1 for a white light single detector integrated system.

1.2 to 30 ═ when the line becomes colored, the variance increases sharply. Tenter films are at least 9 minutes and often much higher. This corresponds to a 0.5 to 1 on a 0 to 1 scale: a situation arising from a white light single detector integrated system.

After carrying out the above process, the processor is operable to compare the values (or spectra) calculated using the process (which represent the received signals) with a set of predefined values stored in a database (not shown). These predefined values (or predefined spectra) correspond to the filtered transmitted radiation FTL values (when the wavelength-specific filtering element 518 is employed) or predefined spectra that are expected when an authentic article (e.g., an authentic film) is positioned in the measurement region.

After performing the comparison, the processor 504 is operable to command the alarm system 506 to indicate that the film/article is authentic or non-authentic. If the result of the comparison is positive (i.e., the film is authentic), the processor is operable to send a signal to the alarm system 506 containing a command to issue an indication that the film/article is authentic. Otherwise, the processor is operable to send a signal to the alarm system 506 containing a command to issue an indication that the film/article is not authentic.

In an optional arrangement of the arrangements illustrated in fig. 7a and 7b, instead of a single second polarizer being rotatable between an orientation in which the direction of polarisation is crossed relative to the direction of the first polarizer and an orientation in which the direction of polarisation is the same as the direction of the first polarizer, the second polarizer may actually comprise two separate second polarizers having different orientations, which may be placed in the beam path depending on which type of transmission is required (i.e. crossed polarisation compared to the first polarizer, or parallel polarisation compared to the first polarizer).

In an optional arrangement of the arrangement illustrated in fig. 10, a white light emitter source may be used in conjunction with a spectrometer as the detector 516. In such an arrangement, the wavelength filtering element 518 is not required.

In another optional arrangement of the arrangement illustrated in fig. 10, the emitter 510 may comprise a white light source and the detector 516 may comprise an array of photodiodes with a corresponding array of wavelength filtering elements 518 (optionally, different color filters). For example, apparatus 500 may include a white LED as emitter 510 and three photodiodes to be effective as detectors 516. A first of the three photodiodes may have a corresponding blue filter as its associated wavelength filtering element 518, a second of the three photodiodes may have a corresponding green filter as its associated wavelength filtering element 518, and a third of the three photodiodes may have a corresponding red filter as its associated wavelength filtering element 518.

In another optional arrangement of the arrangement illustrated in fig. 10, the emitter 510 may comprise an array of emitters, each emitter operable to emit a different color of light. The detector 516 may include an array of corresponding detectors, each responsive to light of a particular color emitted by an associated one of the array of emitters.

In another optional arrangement of the arrangement illustrated in fig. 10, the emitter 510 may comprise an electromagnetic emitter source or array of sources that is controllable to emit white light, light of a particular color (i.e., light in a particular wavelength range of the visible electromagnetic spectrum), and/or light of a mixed color (but not all colors). This may be implemented using one type of white light LED that includes red, green, and blue LEDs positioned in a white light LED housing. Red, green, and blue LEDs may be illuminated together to produce white light. However, by adapting the white LEDs such that each of the red, green and blue LEDs is individually controllable, white light, colored light (e.g., only red, only blue or only green) or mixed color light (e.g., red and green light, blue and red light) can be obtained by controlling which LEDs (or combinations of LEDs) are illuminated.

This optional arrangement of the arrangement illustrated in fig. 10 may be suitable for determining whether the tested membrane is of a first type or other type or at least a second type or other type. The first type of film can be, for example, a film formed using a bubble process. At least the second type of film can be a film formed, for example, using a tentering process. The apparatus may be employed to identify a first type of genuine film, at least a second type of genuine film and a non-genuine film.

The arrangement will be described further with reference to fig. 13 to 16.

Fig. 13 schematically illustrates a perspective view of an optional arrangement of the apparatus illustrated in fig. 10. In this optional arrangement, the emitter 510 comprises an electromagnetic emitter source that is controllable to emit White Light (WL) or a particular Color of Light (CL) depending on the mode of operation.

Different emitter sources will produce different intensity versus delay curves. Thus, the intensity versus delay profile in which the emitter sources emit white light will be different than the intensity versus delay profile in which the emitter sources emit colored light.

Fig. 14 illustrates a graph of delay versus intensity as measured by the detector 516 of the apparatus when the apparatus 500 of fig. 13 is operated in the first mode such that the emitter 510 emits white light and the detector 516 receives white light (PTL). Fig. 15 illustrates a delay versus intensity plot as measured by the detector 516 of the device of fig. 13 when the device 500 is operated in the second mode such that the emitter 510 emits a colored light and the detector 516 receives a colored light (PTL). Fig. 16 illustrates a combined view of the views of fig. 14 and 15.

The intensity curve illustrated in fig. 14 corresponds to the intensity of electromagnetic radiation received by the detector 516 for different film types (i.e., different retardation values) when the emitter 510 is operated in the first mode to emit white light. Polymer films made using the bubble process will generally have retardation values in the range 0 to 120nm (represented by box R in fig. 14). As can be seen from the curves illustrated in fig. 14, the intensity signal for polymer films having retardation values within this range will be relatively low compared to films having higher retardation values.

Thus, the arrangement may be used to determine if the film under test is a film manufactured using a bubble process (i.e., a film having a low retardation value) if the intensity value of white light electromagnetic radiation received by the detector is less than 0.2. Thus, in the first mode of operation, if the intensity value is less than 0.2, the apparatus 500 may classify the film under test as a first type (i.e., as made using a bubble process), or if the intensity value is greater than 0.2, the apparatus 500 may classify the film under test as at least a second type or some other type.

In some instances, it may be desirable to determine the authenticity of an article that includes a polymeric substrate (e.g., a tentered film) that has been formed by a non-bubble process. If the device 500 is to be used in this manner, the first mode measurement and the second mode measurement are used by each other to make an authenticity determination.

Very common polymer films made using a tenter frame process will generally have a thickness in the range 900 to 1100nm (from block S)₁) The delay value of (1). Referring again to fig. 14, it can be seen that a film having a retardation value in this range will produce a received intensity of white light at detector 516 (when the device is operated in the first mode) with a value between 0.5 and 0.6. However, and as can be seen from the figure, at both higher and lower retardation values, intensity values of 0.5 to 0.6 are very common across the spectrum. Indeed, such intensity values may also occur, where the film under test has a retardation between: about 1400nm to about 1700nm (from box S)₂Represents); about 2100nm to about 2400nm (from box S)₃Represents); about 2800nm to about 3200nm (from box S)₄Represents); and about 3500nm to about 3900nm (by box S)₅Representation).

Thus, as will be appreciated, using an intensity value between 0.5 and 0.6 will not permit determination of the retardation value of the film under test, since received white light electromagnetic radiation at values in this range correspond to a plurality of possible film retardation values.

While intensity value ranges of 0.5 and 0.6 may be used to exclude intensity values that result outside this range (as mentioned above), additional steps are required to determine whether the film under test has a retardation value within the desired range.

To summarize the process so far, if the intensity value of the white light received by the detector 516 is less than 0.2 (i.e., the first mode first threshold), then the apparatus 500 indicates that the film under test is of the first type (i.e., bubble process film). If the intensity value of the white light received by the detector 516 is between 0.5 and 0.6 (i.e., above the first threshold but between the first mode second threshold and the first mode third threshold), the apparatus 500 must proceed to a second mode of operation (described further below) in order to make a determination of the retardation value (and thus whether the film is of the second type). If the intensity value of the white light received by detector 516 is both greater than the first mode first threshold (i.e., 0.2) and outside of the range of values between the first mode second threshold (i.e., 0.5) and the first mode third threshold (i.e., 0.6), then apparatus 500 is operable to indicate that the film under test is of a non-true type.

The second mode of operation will be described with respect to fig. 15. In this mode of operation, the emitter 510 operates to emit colored light using two light sources (a source emitting light at 490nm and a source emitting light at 540 nm). Of course, in other arrangements, different sources operable to emit light at different wavelengths may be used.

Thus, the intensity profile in FIG. 15 corresponds to the colored light received at the detector 516 using the source described above as the emitter 510. Again, a polymer film manufactured using a bubble process and having retardation values in the range of 0 to 120nm is represented in this figure by block R.

Made using a tenter process and having retardation values in the range 900 to 1100nm (indicated by box T in this figure)₁Etc.) will produce an intensity value of about 0.1 to 0.2 at detector 516. As can be seen from FIG. 15, there are two other ranges of film retardation values that will yield 0.1 to 0 at the detector 516Approximately equivalent intensity values of 2. These are: retardation values in the range 50 to 120nm (i.e., within box R corresponding to the bubble process film); and in the range of about 450nm to about 600nm (i.e., in this figure by box T)₂To represent) delay value. However, when intensity value measurements from the first mode of operation are also considered, processor 504 may be excluded from both block R and block T₂Delay values in a range of. These processing steps can be seen by overlaying the intensity curve of fig. 14 on the intensity curve of fig. 15, as illustrated in fig. 16.

In FIG. 16, block S₁&T₁Representing a combination of parameters from both the first and second modes of operation. That is, if the film under test produces an intensity value that satisfies the boundary parameter for both the first mode of operation and the second mode of operation, the apparatus determines that the film under test is of the second type (i.e., in this example, a true tenter film).

Thus, if the intensity value of the white light received by detector 516 is between 0.5 and 0.6 in the first mode of operation (i.e., above the first threshold but between the first mode second threshold and the first mode third threshold), then apparatus 500 proceeds to implement the second mode of operation. If the intensity value of the colored light received by the detector 516 in the second mode of operation is between about 0.1 (second mode first threshold) and about 0.2 (second mode second threshold), the apparatus 500 is operable to determine that the film under test is of the second true type (e.g., a true tenter film). However, if, after implementing the second mode of operation, the intensity value of the colored light received by the detector 516 is outside the range of values between the second mode first threshold (i.e., 0.1) and the second mode second threshold (i.e., 0.2), then the apparatus 500 is operable to indicate that the film under test is of the true type.

The above algorithm implemented by processor 504 may be summarized as follows:

mode 1 (white light)

a) If the intensity value at the detector is less than about 0.2, the apparatus is operable to provide an indication that the film is genuine and of the first type; or

b) If the intensity value at the detector is between about 0.5 and about 0.6, then the apparatus is operable to implement mode 2; or

c) If the intensity value at the detector is greater than about 0.2 and not between about 0.5 and 0.6, the apparatus is operable to provide an indication that the film is non-authentic;

mode 2 (colored light)

a) If the intensity value at the detector is between about 0.1 and about 0.2, the apparatus is operable to provide an indication that the film is genuine and of a second type; or

b) If the intensity value at the detector is not between about 0.1 and about 0.2, the apparatus is operable to provide an indication that the film is non-authentic.

It should be appreciated that the apparatus 500 may be configured to detect other pellicle types by merely altering the threshold in the first and/or second modes of operation. That is, the techniques employed by apparatus 500 may be used to determine the authenticity of films having any range of retardation values.

In addition, the apparatus 500 may be configured to illuminate the sample film under test using different color light source combinations. Thus, instead of a white light source in the first mode and a colored light source in the second mode, the device may employ a first colored light source in the first mode and a second colored light source in the second mode. Optionally, there may be more than two modes of operation, e.g., a first colored light source may be operated in a first mode, a second colored light source may be operated in a second mode, a third colored light source may be operated in a third mode, etc.

In one or more of the above embodiments, the authentication device may further include: a data storage element (e.g., ROM) for storing predetermined birefringence characteristic data and other optical characteristic data; and a working memory or cache memory (e.g., RAM).

In yet further optional arrangements, one or more of the features of one or more of the embodiments described above (as illustrated in fig. 4 a-4 b, 5, 6, 7, 8, 9, 10 and 13) may be employed in different combinations to form further embodiments of the authentication apparatus.

In one or more of the illustrated embodiments, a point-type electromagnetic radiation emitting source and a point-type detector are shown. However, in an optional arrangement, a linear electromagnetic radiation emitting source and/or a linear detector may be used.

In yet further optional arrangements, a point-type source, a linear source, a combination of point-type detectors, and/or linear detectors may be used.

In the description above, any reference to "light" is intended to encompass electromagnetic radiation not only in the "visible" portion of the electromagnetic spectrum, but also in the "non-visible" portion of the electromagnetic spectrum. Additionally, any reference to the "visible" portion of the electromagnetic spectrum is intended to encompass infrared light and ultraviolet light.

Insofar as embodiments of the invention described above can be implemented, at least in part, using a software-controlled programmable processing apparatus (e.g., a general-purpose or special-purpose processor, digital signal processor, microprocessor or other processing apparatus, data processing device, or computer system), it will be appreciated that a computer program for configuring a programmable apparatus, device, or system to implement the method and device is envisaged as an aspect of the invention. The computer program may be embodied as any suitable type of code, such as source code, object code, compiled code, interpreted code, executable code, static code, dynamic code, and the like. The instructions may be implemented using any suitable high-level, low-level, object-oriented, visual, compiled and/or interpreted programming language (e.g., Liberate, OCAP, MHP, Flash, HTML and associated languages, JavaScript, PHP, C + +, Java, BASIC, Perl, Matlab, Pascal, visual BASIC, Java, ActiveX, assembly language, machine code, etc.). The skilled person will readily understand that the term "computer" encompasses programmable devices (e.g. the ones referred to above) as well as data processing apparatus and computer systems in their most general sense.

Suitably, the computer program is stored in machine-readable form on a carrier medium, which may include, for example, memory, removable or non-removable media, erasable or non-erasable media, writeable or re-writeable media, digital or analog media, hard disk, floppy disk, compact disk read Only memory (CD-ROM), compact disk recordable (CD-R), compact disk Rewriteable (CD-RW), optical disk, magnetic disk, magneto-optical media, removable memory cards or disks, various types of Digital Versatile Disk (DVD) subscriber identity modules, magnetic tape, or solid state memory cartridges.

As used herein, any reference to "one embodiment" or "an embodiment" means that a particular element, feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment. The appearances of the phrase "in one embodiment" in various places in the specification are not necessarily all referring to the same embodiment.

As used herein, the terms "comprises," "comprising," "includes," "including," "has," "having" or any other variation thereof, are intended to cover a non-exclusive inclusion. For example, a process, method, article, or apparatus that comprises a list of elements is not necessarily limited to only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. In addition, unless expressly stated to the contrary, "or" means an inclusive or and not an exclusive or. For example, any one of the following satisfies condition a or B: a is true (or present) and B is false (or not present); a is false (or not present) and B is true (or present); and both a and B are true (or present).

Additionally, the use of "a" or "an" is used to describe elements and components of the invention. This is done merely for convenience and to give a general sense of the invention. Such description should be understood to include one or at least one and the singular also includes the plural unless it is clearly intended to the contrary.

In view of the foregoing description it will be evident to a person skilled in the art that various modifications may be made within the scope of the invention.

The scope of the present disclosure includes any novel feature or combination of features disclosed herein either explicitly or implicitly or any generalisation thereof, whether or not it relates to the claimed invention or mitigates any or all of the problems addressed by the present invention. The applicants hereby give notice that new claims may be formulated to such features during the prosecution of the present application or of any such further application derived therefrom. In particular, with reference to the appended claims, features from dependent claims may be combined with those from the independent claims and features from respective independent claims may be combined in any suitable manner and not merely in the specific combinations enumerated in the claims.

Claims

1. An authentication apparatus operable to determine authenticity of a polymer film, comprising an optically-based birefringence measurement arrangement operable to measure a first effect influenced by a birefringence characteristic of the film from a first angle comprising a non-perpendicular angle to a plane of the film, and at least one of a second angle and a third angle; and wherein the apparatus is operable to:

comparing a value or range of values representative of the first effect measured from the first angle to a value or range of values representative of a specified first effect corresponding to a predetermined birefringence characteristic of an authentic polymer film for the first angle;

comparing a value or range of values representative of the first effect measured from the at least one of the second and third angles to a value or range of values representative of a specified first effect corresponding to a predetermined birefringence characteristic of an authentic polymer film for the respective second and/or third angles; and

outputting an authenticity signal indicative of authenticity or otherwise of the film based on the comparison.

2. The apparatus of claim 1, wherein the second angle comprises a non-perpendicular angle to a plane of the film and the third angle comprises a perpendicular angle to a plane of the film.

3. Apparatus according to claim 1 or 2, wherein the apparatus is operable to distinguish between membranes made by a bubble process and membranes made by different processes.

4. The apparatus according to any of the preceding claims, wherein the optical-based birefringence measurement arrangement comprises: an emitter positioned and operable to illuminate a first side of the film positioned in a measurement region of the apparatus with electromagnetic radiation; a first polarizer positioned between the first emitter and the first side of the film such that at least a portion of electromagnetic radiation emitted by the first emitter passes therethrough; a first detector positioned on a second side of the film and operable to receive electromagnetic radiation from the emitter that is transmitted through the film and transmitted from the second side of the film at the first angle and at least one of the second angle and the third angle; a second polarizer positioned between the second side of the film and the first detector such that at least a portion of electromagnetic radiation transmitted through the film passes therethrough, wherein the first detector is operable to output a signal representative of the first effect measured based on electromagnetic radiation transmitted from the second side of the film at the first angle and at least one of the second angle and the third angle.

5. The apparatus of claim 4, wherein the first detector is movable relative to the second side of the film to be positioned at a first position to receive electromagnetic radiation from the emitter that is transmitted through the film and transmitted from the second side of the film at the first angle, and is further movable to a second position and/or a third position to receive electromagnetic radiation from the emitter that is transmitted through the film and transmitted from the second side of the film at the respective second and/or third angle.

6. The apparatus of claim 4, further comprising:

a second detector positioned on a second side of the film and operable to receive electromagnetic radiation from the emitter that is transmitted through the film and transmitted from the second side of the film at the second angle; and/or

A third detector positioned on a second side of the film and operable to receive electromagnetic radiation from the emitter that is transmitted through the film and transmitted from the second side of the film at the third angle;

wherein:

the second detector is operable to output a signal representative of the first effect measured based on electromagnetic radiation transmitted from the second side of the film at the second angle; and/or

The third detector is operable to output a signal representative of the first effect measured based on electromagnetic radiation transmitted from the second side of the film at the third angle.

7. The apparatus of any preceding claim, wherein the first angle comprises one of: (i) an angle described by a vector [101] with respect to the film; and (ii) an angle described by the vector [111] with respect to the film.

8. The apparatus of claim 7, any one of the preceding claims, wherein the second angle comprises the other of: (i) an angle described by a vector [101] with respect to the film; and (ii) an angle described by the vector [111] with respect to the film.

9. The apparatus of any of claims 4 to 8, wherein an output signal output by the first detector is proportional to an intensity of the received transmitted electromagnetic radiation.

10. The apparatus of claim 9, wherein the first detector is operable to communicate the output signals to a processor operable to compare values of the output signals representing the first effect measured from the first angle to the value or range of values representing a specified first effect corresponding to a predetermined birefringence characteristic of an authentic polymer film for the first angle.

11. The apparatus of claim 10, wherein the value or range of values comprises at least one expected first detector output signal value representative of electromagnetic radiation transmitted from the second side of the film at the first angle and received by the first detector if a real film is positioned in the measurement region.

12. The apparatus of claim 6 or any of claims 7 to 11, when dependent directly or independently on claim 6, wherein the output signal output by the second detector and/or the third detector is proportional to the intensity of the received transmitted electromagnetic radiation.

13. The apparatus of claim 12, wherein:

the second detector is operable to communicate the output signals to a processor operable to compare values of the output signals representing the first effect measured from the second angle to the value or range of values representing a specified first effect corresponding to a respective predetermined birefringence characteristic of an authentic polymer film for the second angle; and/or

The third detector is operable to communicate the output signals to a processor operable to compare values of the output signals representing the first effect measured from the third angle to the value or range of values representing a specified first effect corresponding to a respective predetermined birefringence characteristic of an authentic polymer film for the third angle.

14. The apparatus of claim 13, wherein:

the value or range of values comprises at least one expected second detector output signal value representative of electromagnetic radiation transmitted from the second side of the film and received by the second detector with an actual film positioned in the measurement region; and/or

The value or range of values includes at least one expected third detector output signal value representative of electromagnetic radiation transmitted from the second side of the film and received by the third detector with an actual film positioned in the measurement region.

15. The apparatus of any preceding claim, further comprising an optical-based measurement arrangement operable to measure a second effect affected by at least one other optical characteristic of the film at the first angle comprising a non-perpendicular angle to a plane of the film and at least one of the second and third angles, and wherein the apparatus is operable to:

comparing a value or range of values representing the second effect as measured at least one of the first angle and the second and third angles comprising a non-perpendicular angle to a surface of the film with a value or range of values representing a specified second effect corresponding to a predetermined other optical property of an authentic polymer film for the respective first angle and the respective second and/or third angle, and

outputting an authenticity signal indicative of authenticity or otherwise of the film based on:

comparing birefringence measurements according to any of the preceding claims; and/or

The comparison of the value or range of values of the second effect, as measured at the first angle and at least one of the second and third angles comprising a non-perpendicular angle to the plane of the film, with a corresponding value or range of values representative of the specified second effect corresponding to a predetermined other optical characteristic of an actual polymer film for the corresponding first angle and the corresponding second and/or third angle.

16. Apparatus according to claim 15 when dependent directly or independently on claim 4, wherein the second polariser is controllably orientated to achieve polarisation in one of: a first direction transverse to the direction of the first polarizer; and a second direction that is the same as the direction of the first polarizer; wherein the first detector and/or optionally the second detector and/or the third detector is operable to: measuring the first effect affected by the birefringence characteristic of the film when the second polarizer is oriented to achieve polarization in the first direction that is transverse to the direction of the first polarizer; and measuring the second effect affected by the other optical characteristic of the film when the second polarizer is oriented to achieve polarization in the second direction that is the same as the direction of the first polarizer.

17. The apparatus of claim 16, wherein the first detector and/or optionally second detector and/or third detector is operable to: outputting a first signal representative of the first effect as measured; and outputting a second signal representative of the second effect as measured.

18. The apparatus of claim 17, wherein the first and second output signals output by the first and/or optionally second and/or third detectors are proportional to the intensity of the received transmitted electromagnetic radiation.

19. The apparatus of claim 17 or 18, wherein the first and/or optionally second and/or third detector is operable to communicate the first and second output signals to a processor operable to:

comparing a value of the first output signal to a value or range of values representative of the specified first effect; and

comparing a value of the second output signal to a value or range of values representing the specified second effect, the specified second effect corresponding to a predetermined film transmittance.

20. The apparatus of claim 19, wherein if the first output signal value or range of values has a level that is distinguishable from a first output signal value or range of values representing an effect affected by a background condition, the processor is operable to output the authenticity signal based on a comparison of the value or range of values of the second output signal with the value or range of values representing the specified second effect.

21. The apparatus of claim 19 or 20, wherein the value or range of values comprises at least one expected first detector and/or optionally second detector and/or third detector output signal value representative of electromagnetic radiation transmitted from the second side of the film and received by the first detector and/or optionally second detector and/or third detector when the second polarizer is oriented to achieve polarization in the first direction and in the second direction, respectively, with an actual film positioned in the measurement region.

22. The apparatus of any of claims 19 to 21, wherein the processor is operable to:

calculating a difference between a value of the first output signal and a value of the second output signal;

calculating a modified difference value by halving the difference value;

calculating a birefringence representation value by subtracting the modified difference value from the second output signal value;

comparing the birefringence representation value to the value or range of values representing the specified first effect; and

outputting the authenticity signal indicative of authenticity or otherwise of the film based on the comparison.

23. The apparatus of any of the preceding claims, wherein the optically-based birefringence measurement arrangement is further operable to measure a third effect influenced by the birefringence characteristic of the film within at least a portion of the electromagnetic spectrum and at least one of the first angle and the second and third angles, and wherein the apparatus is operable to:

comparing a value or range of values representative of the third effect as measured at the first angle and at least one of the second and third angles to a corresponding value or range of values representative of a specified third effect corresponding to a predetermined birefringence characteristic of an authentic polymer film at the corresponding first angle and the corresponding second and/or third angles for the same at least a portion of the electromagnetic spectrum; and

24. The authentication device of claim 23, wherein the measurement of the third effect comprises a monochromatic measurement.

25. Apparatus according to claim 23 or 24 when dependent directly or independently on claim 4, wherein the first and/or optionally second and/or third detectors are configured to selectively respond to the at least part of the electromagnetic spectrum.

26. The apparatus of claim 25, wherein the first and/or optionally second and/or third detectors are controllable to alter their detection range to correspond to the at least a portion of the electromagnetic spectrum.

27. The apparatus of claim 25, wherein the first detector and/or optionally second detector and/or third detector are preselected to detect electromagnetic radiation from the at least a portion of the electromagnetic spectrum.

28. Apparatus according to any one of claims 23 to 27 when dependent directly or independently on claim 4, wherein each of the first and/or optionally second and/or third detectors comprises an array of at least two sub-detectors, a first of the at least two sub-detectors being operable to detect electromagnetic radiation from a first portion of the electromagnetic spectrum and a second of the at least two sub-detectors being operable to detect electromagnetic radiation from a second portion of the electromagnetic spectrum.

29. The apparatus of claim 28, wherein the first sub-detector is controllable to alter its detection range to correspond to the first portion of the electromagnetic spectrum, and the second sub-detector is controllable to alter its detection range to correspond to the second portion of the electromagnetic spectrum.

30. The apparatus of claim 28, wherein the first sub-detector is preselected to detect electromagnetic radiation from the first portion of the electromagnetic spectrum and the second sub-detector is preselected to detect electromagnetic radiation from the second portion of the electromagnetic spectrum.

31. Apparatus according to any one of claims 23 to 27, when dependent directly or independently on claim 4, further comprising at least one filter arranged to mask at least another portion of the electromagnetic spectrum and transmit the at least one portion of the electromagnetic spectrum for reception by the first and/or optionally second and/or third detectors.

32. Apparatus according to any one of claims 23 to 31 when dependent directly or independently on claim 4, wherein the emitter or optionally emitters are controllable to emit electromagnetic radiation in said at least part of the electromagnetic spectrum.

33. The apparatus of any one of claims 23 to 31, when dependent directly or independently on claim 5, wherein the emitter or optionally emitters are preselected to emit electromagnetic radiation in the at least a portion of the electromagnetic spectrum.

34. The apparatus of claim 32 or 33, wherein the emitter or optionally emitters are operable in a first mode to emit white light and in a second mode to emit colored light.

35. The apparatus of claim 32 or 33, wherein the apparatus is operable in a first mode to control a first emitter to emit white light and in a second mode to control a second emitter to emit colored light.

36. Apparatus according to claim 34 or 35, wherein in the first mode the apparatus is operable to indicate whether the polymer film under test comprises a first true type or at least a second true type based on the output signal of the first detector, and further wherein in response to an output signal indicating that the polymer under test is a type different from the first true type, the apparatus is operable to implement the second mode and to indicate whether the polymer film under test comprises the at least second true type or another type of polymer film based on the output signals of the first detector in both the first and second modes.

37. The apparatus of claim 36, wherein in the first mode, the apparatus is operable to:

comparing the value or range of values representing the third effect as measured at the first angle and at least one of the second and third angles to the value or range of values representing a specified third effect corresponding to a predetermined birefringence characteristic of a first genuine type of polymer film at the respective first and second and/or third angles; and

outputting a classification signal indicating that the membrane includes a first true type or other type based on the comparison.

38. The apparatus of claim 37, wherein the apparatus is operable to: outputting a classification signal indicating that the film comprises a first true type if the value representing the third effect as measured at the first, second or third angle is below a corresponding first mode first threshold value for the first, second or third angle, the corresponding first mode first threshold value representing an upper limit of the specified first effect for the first true type of film.

39. The apparatus of claim 38, wherein the apparatus is operable to: in case the value representing the third effect as measured at the first, second or third angle is both above the corresponding first mode first threshold for the first, second or third angle and not within a value range between a corresponding first mode second threshold for the first, second or third angle and a corresponding first mode third threshold for the first, second or third angle, outputting a classification signal indicating that the film comprises a non-true type.

40. The apparatus of claim 39, wherein the apparatus is operable to: implementing the second mode if the value representative of the third effect as measured in the first mode at the first, second, or third angle is between the corresponding first mode second threshold for the first, second, or third angle and the corresponding first mode third threshold for the first, second, or third angle.

41. The apparatus of claim 40, wherein the apparatus is operable to: outputting a classification signal indicating that the film comprises a second true type if the value representing the third effect as measured at the first, second or third angle is within a range of values between a corresponding second mode first threshold for the first, second or third angle and a corresponding second mode second threshold for the first, second or third angle, the range of values representing a specified third effect for the second true type of film.

42. The apparatus of any preceding claim, further comprising an optically-based birefringence imaging arrangement for imaging a birefringence pattern of the film at the first angle and at least one of the second and third angles, and wherein the apparatus is operable to:

comparing an image of the birefringence pattern with a corresponding image representing a predetermined birefringence pattern of an authentic polymer film at the corresponding first angle and the corresponding second and third angles; and

43. The apparatus of claim 42, wherein the optical-based birefringence imaging arrangement comprises: an emitter positioned and operable to illuminate the first side of the film positioned in a measurement region of the apparatus with electromagnetic radiation; a first polarizer positioned between the first emitter and the first side of the film such that at least a portion of electromagnetic radiation emitted by the first emitter passes therethrough; an imaging device positioned on a second side of the film and operable to receive electromagnetic radiation from the emitter that is transmitted through the film and transmitted from the second side of the film; a second polarizer positioned between the second side of the film and the imaging device such that at least a portion of electromagnetic radiation transmitted through the film passes therethrough, wherein the imaging device is operable to: outputting data representing an imaged birefringence pattern based on electromagnetic radiation transmitted from the second side of the film and received at the imaging device.

44. An apparatus according to claim 43, wherein the imaging device is operable to output the data representing an imaged birefringence pattern to a processor operable to compare the output data with a data set representing a predetermined birefringence pattern.

45. The apparatus according to claim 43 or 44, wherein at least one of the emitter, the first polarizer and the second polarizer has in common with that/those of the optical based birefringence measurement arrangement and/or the optical based measurement arrangement.

46. The apparatus of any of claims 43-45, wherein the emitter comprises a white light source.

47. The apparatus of any of claims 43-46, wherein the imaging device comprises a photosensitive array.

48. The apparatus of any preceding claim, further comprising an optical response modifier arranged to modify the first effect to introduce a predetermined amount of offset to the value or range of values representative of the effect as measured, wherein the optical-based birefringence measurement arrangement is operable to measure the first effect as modified.

49. A device according to claim 48 when dependent directly or independently on claim 4, wherein the optical response modifier is positioned in a beam path of electromagnetic radiation between the emitter and the first and/or optionally second and/or third detector, and further wherein the first and/or optionally second and/or third detector is operable to measure the first effect.

50. An apparatus as claimed in claim 49, wherein the first and/or optionally second and/or third detectors are operable to output a signal representative of the first effect as modified.

51. The apparatus of claim 49 or 50, wherein the first detector and/or optionally second detector and/or third detector is operable to communicate the output signal to a processor operable to compare a value of the output signal representing the first effect as modified to a value or range of values representing a specified first effect corresponding to a predetermined birefringence characteristic of an authentic polymer film and as modified by the same optical response modifier.

52. The apparatus of any preceding claim, wherein the apparatus is operable to receive an article comprising a polymeric film forming at least a portion of a substrate of the article.

53. Banknote validating apparatus comprising an apparatus according to any one of the preceding claims, wherein the apparatus is operable to determine the authenticity of a banknote comprising a polymeric film forming at least a portion of a substrate of the banknote.

54. Use of the apparatus according to any one of claims 1 to 52 to determine the authenticity of a polymer film.

55. A method of determining the authenticity of a polymer film, comprising:

measuring a first effect affected by a birefringence characteristic of the film from a first angle comprising a non-perpendicular angle to a plane of the film, and at least one of a second angle and a third angle;

56. The method of claim 55, wherein the second angle comprises a non-perpendicular angle to a plane of the film and the third angle comprises a perpendicular angle to a plane of the film.

57. The method of claim 55 or 56, further comprising indicating whether the polymer film is made by a bubble process or a different process.

58. The method of any of claims 55 to 57, further comprising:

illuminating a first side of the film positioned in a measurement area of the device with electromagnetic radiation polarized by a first polarizer positioned between a first emitter and the first side of the film such that at least a portion of the electromagnetic radiation emitted by the first emitter passes therethrough;

receiving, at a first detector positioned on a second side of the film, electromagnetic radiation from the emitter transmitted through the film at the first angle and at least one of the second angle and the third angle and polarized by a second polarizer positioned between the second side of the film and the first detector; and

outputting a signal representing a first effect as measured based on electromagnetic radiation transmitted from the second side of the film at the first angle and at least one of the second angle and the third angle.

59. The method of claim 58, further comprising: positioning the first detector at a first position to receive electromagnetic radiation from the emitter that is transmitted through the film and transmitted from the second side of the film at the first angle; and moving the first detector to a second position and/or a third position to receive electromagnetic radiation from the emitter that is transmitted through the film and transmitted from the second side of the film at the respective second angle and/or third angle.

60. The method of claim 58, further comprising:

providing a second detector on a second side of the film for receiving electromagnetic radiation from the emitter that is transmitted through the film and transmitted from the second side of the film at the second angle; and/or providing a third detector positioned on a second side of the film for receiving electromagnetic radiation from the emitter that is transmitted through the film and transmitted from the second side of the film at the third angle; and

outputting a signal from the second detector, the signal representing the first effect as measured based on electromagnetic radiation transmitted from the second side of the film at the second angle; and/or

Outputting a signal from the third detector, the signal representing the first effect as measured based on electromagnetic radiation transmitted from the second side of the film at the third angle.

61. The method of any of claims 55 to 60, wherein the first angle comprises one of: (i) an angle described by a vector [101] with respect to the film; and (ii) an angle described by the vector [111] with respect to the film.

62. The method of claim 61, wherein the second angle comprises the other of: (i) an angle described by a vector [101] with respect to the film; and (ii) an angle described by the vector [111] with respect to the film.

63. The method of any of claims 55 to 62, further comprising:

communicating the output signal to a processor;

comparing a value of the output signal representing the first effect as measured from the first angle to the value or range of values representing a specified first effect corresponding to a predetermined birefringence characteristic of an authentic polymer film for the first angle.

64. The method of claim 63, wherein the value or range of values comprises at least one expected first detector output signal value representative of electromagnetic radiation transmitted from the second side of the film at the first angle and received by the first detector with a real film positioned in the measurement region.

65. A method according to claim 60 or any of claims 61 to 64 when dependent directly or independently on claim 60, wherein the output signal output by the second and/or third detector is proportional to the intensity of the received transmitted electromagnetic radiation.

66. The method of claim 65, further comprising:

communicating the output signal from the second detector to the processor;

comparing values of the output signal representing the first effect as measured from the second angle to the values or ranges of values representing a specified first effect corresponding to a respective predetermined birefringence characteristic of an authentic polymer film for the second angle; and/or

Communicating the output signal from the third detector to the processor;

comparing values of the output signal representing the first effect as measured from the third angle to the values or ranges of values representing a specified first effect corresponding to a respective predetermined birefringence characteristic of an authentic polymer film for the third angle.

67. The method of claim 66, wherein:

68. The method of any one of claims 55-67, further comprising:

measuring a second effect affected by at least one other optical characteristic of the film at the first angle and at least one of the second angle and the third angle, including a non-perpendicular angle to a plane of the film;

comparing a value or range of values representing the second effect as measured at the first angle and at least one of the second and third angles with a value or range of values representing a specified second effect corresponding to a predetermined other optical characteristic of an authentic polymer film at the respective first and second and/or third angles; and

The comparison of the value or range of values of the second effect, as measured at the first angle and at least one of the second and third angles, with a corresponding value or range of values representing the specified second effect, the specified second effect corresponding to a predetermined other optical characteristic at the corresponding first and second and/or third angles.

69. The method of claim 68, when dependent directly or independently on claim 58, further comprising:

orienting the second polarizer to achieve polarization in one of: a first direction transverse to the direction of the first polarizer; and a second direction that is the same as the direction of the first polarizer;

measuring the first effect affected by the birefringence characteristics of the film when the second polarizer is oriented to achieve polarization in the first direction transverse to the direction of the first polarizer, and measuring the second effect affected by the other optical characteristics of the film when the second polarizer is oriented to achieve polarization in the second direction that is the same direction as the direction of the first polarizer.

70. The method of claim 69, further comprising: outputting a first signal representative of the first effect as measured; and outputting a second signal representative of the second effect as measured.

71. The method of claim 70, wherein the first and second output signals output by the first and/or optionally second and/or third detectors are proportional to the intensity of the received transmitted electromagnetic radiation.

72. The method of claim 70 or 71, further comprising: communicate the first and second output signals to a processor, and:

73. The method of claim 72, wherein if the first output signal value or range of values has a level distinguishable from a first output signal value or range of values representing an effect affected by a background condition, the processor is operable to output the authenticity signal based on a comparison of the value or range of values of the second output signal with the value or range of values representing the specified second effect.

74. A method according to claim 72 or 73, wherein the value or range of values comprises at least one expected first and/or optionally second and/or third detector output signal value representative of electromagnetic radiation transmitted from the second side of the film and received by the first and/or optionally second and/or third detector when the second polariser is orientated to achieve polarisation in the first and second directions respectively with an actual film positioned in the measurement region.

75. The method of any one of claims 72-74, further comprising:

calculating a modified difference value by halving the difference value;

76. The method of any of claims 55 to 75, further comprising:

measuring a third effect in at least a portion of the electromagnetic spectrum and at least one of the first angle and the second angle and the third angle as affected by the birefringence characteristic of the film;

comparing a value or range of values representative of the third effect as measured at the first angle and the second angle and/or the third angle to a corresponding value or range of values representative of a specified third effect corresponding to a predetermined birefringence characteristic of an authentic polymer film at the corresponding first angle and the corresponding second angle and/or the third angle for the same at least a portion of the electromagnetic spectrum; and

77. The method of claim 76, wherein the measurement of the third effect comprises a monochromatic measurement.

78. The method of claim 76 or 77, when dependent directly or independently on claim 58, further comprising configuring the first and/or optionally second and/or third detectors to selectively respond to the at least a portion of the electromagnetic spectrum.

79. The method of claim 78, further comprising: controlling the first detector and/or optionally the second detector and/or the third detector to alter its detection range to correspond to the at least a portion of the electromagnetic spectrum.

80. The method of claim 78, further comprising: the first detector and/or optionally the second detector and/or the third detector are preselected to detect electromagnetic radiation from the at least a portion of the electromagnetic spectrum.

81. The method of any one of claims 76 to 80 when dependent directly or independently on claim 58, further comprising: providing an array of at least two sub-detectors as each of the first and/or optionally second and/or third detectors; and

detecting electromagnetic radiation from a first portion of the electromagnetic spectrum at a first one of the at least two sub-detectors;

detecting electromagnetic radiation from a second portion of the electromagnetic spectrum at a second of the at least two sub-detectors.

82. The method of claim 81, further comprising: controlling the first sub-detector to alter its detection range to correspond to the first portion of the electromagnetic spectrum; and controlling the second sub-detector to alter its detection range to correspond to the second portion of the electromagnetic spectrum.

83. The method of claim 80, further comprising: preselecting the first sub-detector to detect electromagnetic radiation from the first portion of the electromagnetic spectrum; and pre-selecting the second sub-detector to detect electromagnetic radiation from the second portion of the electromagnetic spectrum.

84. The method of any one of claims 76 to 83 when dependent directly or independently on claim 58, further comprising: masking at least another portion of the electromagnetic spectrum to transmit the at least a portion of the electromagnetic spectrum for reception by the first detector and/or optionally second detector and/or third detector.

85. The method of any one of claims 76 to 84, when dependent directly or independently on claim 58, further comprising: controlling the emitter or optionally emitters to emit electromagnetic radiation in the at least a portion of the electromagnetic spectrum.

86. The method of any one of claims 76 to 84, when dependent directly or independently on claim 58, further comprising: the emitter or optionally emitters are preselected to emit electromagnetic radiation in the at least a portion of the electromagnetic spectrum.

87. The method of claim 85 or 86, further comprising: operating the emitter or optionally emitters in a first mode to emit white light; and operating the emitter or optionally emitters in a second mode to emit colored light.

88. The method of claim 85 or 86, further comprising:

controlling the first emitter to emit white light in a first mode; and

the second emitters are controlled in a second mode to emit colored light.

89. The method of claim 87 or 88, wherein in the first mode, indicating whether the polymer film under test comprises a first true type or at least a second true type of polymer film based on output signals of the first detector and/or optionally a second detector and/or a third detector, and further wherein, in response to an output signal indicating that the polymer under test is of a type other than the first true type, implementing the second mode and indicating whether the polymer film under test comprises the at least second true type or other type of polymer film based on the output signal of the first detector in both the first and second modes and/or optionally the output signal of the second detector and/or third detector in both the first and second modes.

90. The method of claim 89, wherein in the first mode, the method further comprises the steps of:

comparing the value or range of values representing the third effect as measured at the first angle and the second angle and/or the third angle to the value or range of values representing a specified third effect corresponding to a predetermined birefringence characteristic of a first genuine type of polymer film at the respective first angle and the respective second and/or third angle; and

91. The method of claim 90, further comprising: in case the value representing the third effect as measured at the first angle and the second and/or third angle is below a corresponding first mode first threshold value for the first, second or third angle, which represents an upper limit for the specified first effect for the first true type of film, a classification signal is output indicating that the film comprises a first true type.

92. The method of claim 91, further comprising: in case the value representing the third effect as measured at the first angle and the second and/or third angle is both above the corresponding first mode first threshold value for the first, second or third angle and not within a value range between a corresponding first mode second threshold value for the first, second or third angle and a corresponding first mode third threshold value for the first, second or third angle, outputting a classification signal indicating that the film comprises a non-true type.

93. The method of claim 92, further comprising: implementing the second mode if the value representative of the third effect as measured in the first mode at the first angle and the second and/or third angles is between the corresponding first mode second threshold for the first, second or third angle and the corresponding first mode third threshold for the first, second or third angle.

94. The method of claim 93, further comprising: outputting a classification signal indicating that the film comprises a second true type if the value representing the third effect as measured at the first, second or third angle is within a range of values between a corresponding second mode first threshold for the first, second or third angle and a corresponding second mode second threshold for the first, second or third angle, the range of values representing a specified third effect for the second true type of film.

95. The method of any of claims 55 to 94, further comprising:

imaging a birefringence pattern of the film at the first angle and at least one of the second angle and/or the third angle;

comparing the image of the birefringence pattern at the first, second or third angle with a corresponding image representing a predetermined birefringence pattern of an authentic polymer film at the corresponding first, second and third angles; and

96. The method of claim 95, further comprising: outputting data representing the imaged birefringence pattern from the imaging device to a processor; and comparing the output data with a data set representing a predetermined birefringence pattern.

97. The method of claim 95 or 96, further comprising illuminating the film using an emitter comprising a white light source.

98. The method of any one of claims 95 to 97, further comprising providing a photosensitive array to perform the imaging step.

99. The method of any of claims 55 to 98, further comprising: modifying the first effect to introduce a predetermined amount of offset into the value or range of values representing the first effect as measured at the first angle and the second and/or third angles; and measuring the first effect as modified.

100. The method of claim 99, further comprising: communicating the output signal from the first detector and/or optionally second detector and/or third detector to a processor; and comparing a value of the output signal representing the first effect as modified with a value or range of values representing a specified first effect corresponding to a predetermined birefringence characteristic of an authentic polymer film and as modified by the same optical response modifier.

101. A computer program comprising a computer program element operable in a computer processor to implement one or more aspects of the apparatus of any of claims 1 to 54.

102. A computer program comprising a computer program element operable in a computer processor to implement one or more aspects of the method according to any one of claims 55 to 100.

103. A computer readable medium carrying a computer program according to claim 101 or 102.

104. An authentication apparatus substantially as hereinbefore described with reference to and as illustrated in any one or more of figures 4a to 4b, 5, 6, 7a, 7b, 8, 9, 10 and 13 of the accompanying drawings.

105. A method of determining the authenticity of a polymer film substantially as hereinbefore described with reference to and as illustrated in any one or more of figures 4a to 4b, 5, 6, 7a, 7b, 8, 9, 10 and 13 of the accompanying drawings.